nightmare. she screamed, and she yelled, and she cried. it was terrible. did she fall down the steps? no one was thinking someone did this to her, but did someone do this to her? it just unraveled from that moment on. >> the fashionista with red lipstick. she meant the world to me. >> when she walked into a room it was like a movie star walked in. >> corporate executive, caring mom, a million dollar smile and a $4 million estate. >> oh my god! >> i need an ambulance! >> murdered. >> i went screaming out of the house. >> this was a prominent woman murdered in her home late at night. >> almost certainly someone she

knew? >> correct. >> where would it lead? a twisted case of betrayal and greed. >> the finger is being pointed at me. >> her own daughter, a suspect from the start. >> you pull the knife out and you tell the police, oh, you're going to find my fingerprints on the knife. >> her son-in-law, who seemed so devoted. >> they interrogated us for eight hours. >> or maybe someone else with a million dollar motive? >> what's going on here? how many people are involved in this? >> devious. it's an evil mind. >> what pushed you this far? >> i'm lester holt, and this is "dateline." >> someone just doesn't turn into a murderer. >> here's josh mankiewicz with "the evil to come." >> reporter: it was hard to look away when peggy was in the picture. her beauty was captivating, but she was also smart, ambitious, and she loved that little girl. peggy nadell's image survives in

home movies and in memory from the days when she was relishing motherhood blissfully unaware of the evil to come. >> i was always close with my mother. always. >> reporter: susanne nadell-scaccio was that little girl and says her mom peggy was everything a mother should be. >> as a child, i ice skated. my mother would sit in the rink and freeze. she'd sit there with a coat on all bundled up, shivering. >> reporter: susanne and her younger brother jim grew up in suburban rockland county about 45 minutes north of new york city. >> we were able to go away to sleep-away camp when we were little. my parents traveled. >> reporter: at first, peggy did what many women did in the 1960s. she stayed at home while her husband rob headed off to work. but peggy was drawn to something bigger than her suburban sanctuary.

when susanne was young, her mom was back in school earning her mba. >> she was probably one of the few women in the graduating class. >> reporter: and then went into a man's business. >> and then went into a man's business and worked very hard. >> home is where the heinz is. >> reporter: much like the fictional character peggy olson in the hit series, "mad men," the real life peggy broke the glass ceiling at xerox and became a rare member of the executive boys club. anne martin was in that club too. >> you didn't have too many female managers. and peggy, she rose very quickly because she was very intelligent. >> reporter: and always well-dressed. >> peggy wore a lot of black. she loved to dress and wear the latest fashions. >> reporter: unlike her fashionable mom, susanne, was a blue jeans and t-shirt kind of girl. >> susanne -- how do you explain susanne? she's quirky.

she's outgoing. she athletic. >> reporter: darcy greenberg is one of susanne's best friends. >> she's spontaneous. she's talkative. she also likes to be close to home. >> reporter: after college, she came back to rockland county and went to work at xerox herself. one night in a bar susanne, then 21, fell for -- well actually fell over a 17-year-old race car driver named bobby scaccio. >> she actually stepped on me. we were fooling around and i somehow wound up slipping on the floor. she picked me up, and we saw each other and started talking. >> reporter: 13 years later, susanne and bobby, who was by then a welder and steamfitter, were married. peggy was okay about it. it's not unreasonable to believe that maybe she was kind of hoping that her daughter would marry a guy who wore a suit to work.

>> i think so. she was hoping for a harvard son-in-law, but she got a son-in-law from the -- that went to the school of hard knocks, you know? >> reporter: bobby made a good son-in-law. he was always there for peggy, especially after her husband died in 2003. by then peggy was retired but never slowed down. traveling the world and treasuring her family. her son jim was now a psychologist living in florida with his wife diana and her two children. i get the sense that jim was not as close to your parents as you were. >> i'll agree to that. >> and why would that be? >> maybe because of the distance that he was so far away. he did call. he did speak to them. but my brother is my brother. he kind of lived in his own world. >> reporter: but susanne and her mom were very much in the same world. how often did you see your mother? >> almost every day. >> reporter: susanne, always on

the road for her work as marketer for a hospital, would often drop in on her mom. and when she wasn't visiting, she'd be calling. >> speak to her in the afternoon, in the evening. make sure she was home. >> reporter: so it's almost like you were sort of the parent and she was the kid. you were checking up on her. >> oh, absolutely. >> reporter: life was good for the family, until one morning in january of 2014, susanne went to check on her mother. >> oh, my god! oh, my god! oh, my -- i need an ambulance right away. >> reporter: and everything changed. when we come back -- the heartbreaking discovery that sets a mystery in motion. >> i was screaming. >> susanne is in the driveway looking rather frazzled. >> the first thought was, oh, my god, she tripped and she must have hit her head. >> no way did she fall down the stairs. hesitation without any doubt

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♪ saturday, january 25th, 2014, started off cold and snowing. susanne says her day started off as it nearly always did, calling her mother peggy. >> called the cell. she didn't answer. i called the house. she didn't answer. i said, all right. maybe she's in the bathroom or she went out into the garage for something. >> reporter: susanne, who lives in a suburb of new york city, called diana, her sister-in-law in florida. >> and i said, have you spoken with mommy this morning? she said, you know, i called her at 7:30 and i haven't heard back from her.

>> reporter: now worried, susanne got in her car and drove to peggy's house. >> as i'm driving, i'm calling the house, the cell, the house, the cell. no answer. and now i'm getting panicky. i pull into her driveway, and i saw the roof of her car through the garage door. and i said, oh, this is not going to be good. >> reporter: she was right. susanne says she found peggy crumpled at the bottom of the stairs with a knife in her chest. >> and the first thought was, oh, my god. she tripped on the cat and fell and stuck herself. >> reporter: then she says she saw the blood. >> and i said, oh, my god, she must have hit her head when she fell. >> reporter: and then susanne did something that would later raise a number of questions. >> i pulled the knife. i was gonna do cpr. >> reporter: you pulled the knife out of her? >> yeah. if your mother was laying there with something sticking out of her that was hurting her, what would you do? you'd want to make that hurt go away. >> reporter: could you tell whether she was dead or alive? >> when i touched her neck and

she was kind of cold. >> reporter: susanne ran out of the house and called 911. >> oh, my god! oh, my god! oh, my god. >> rockland 911. what is the address of your emergency? >> i was screaming. i'm sure the neighbors that were around heard. i need an ambulance right away! >> ma'am calm down. what's going on there? >> i think my mother fell down the stairs with a knife in her hand and stabbed herself. >> reporter: susanne was right about one thing. peggy nadell was dead. her next call was to her brother jim in florida. >> i called my brother's house. he didn't answer. i called diana on her cell, and i said, mommy's gone. and she started screaming at the other end of the phone. what do you mean mommy's gone? i said, she's gone. she died. something happened. she died. >> reporter: soon clarkstown police detectives stephen cole-hatchard and earl lorence were on the scene. they noticed that susanne looked a wreck, standing in front of the house in the snow. >> susanne is in the driveway, at the foot of the driveway, kind of pacing, looking rather frazzled.

>> reporter: she told detectives what she told the 911 operators, that peggy tripped over the cat. >> her mother must have tumbled down the stairs and stabbed herself with the knife. >> reporter: while detective cole-hatchard stayed outside with susanne, detective lorence went inside the house. this is police video of the scene taken that morning. lorence knew right away, this was no accident. >> no way did she fall down the stairs and trip over a cat. >> reporter: detective lorence saw peggy had been strangled, then stabbed. and it also looked as if she'd been beaten with a statue head found under her body and a gold metal ball near her hand. >> the crime scene itself was very concentrated. everything was at the bottom of the stairs and in the bedroom upstairs. >> reporter: something else caught the detective's attention -- two chairs were pulled out at the kitchen table,

as if peggy had been sitting and talking with someone. peggy's computer, wallet and jewelry were missing. a jewelry box lay near a chair in the living room, empty. but to earl lorence, the burglary looked phony. staged. >> the bedroom drawers, they were neatly pulled out and neatly placed on the floor in front of the dresser. at normal burglary scenes stuff is everywhere. >> reporter: people go through it like a tornado. >> correct. >> reporter: and this wasn't a break-and-enter job. police could tell that when they looked at the fresh snow outside the house. >> there was one set of footprints, and that was the responding officer checking the perimeter of the home. >> reporter: so nothing suggesting that somebody had walked around, cased the place? >> not a thing. >> reporter: the front door hadn't been jimmied or broken in. >> there was a key in the deadbolt in the front door that's required to open the door from the inside. and that was in the lock. >> reporter: meaning peggy had unlocked it from inside? >> correct. >> reporter: that afternoon

detectives brought susanne and her husband bobby to the police station and started asking questions. >> you called your mother from the car? >> yeah. >> okay. >> reporter: susanne told them contractors had been doing work on peggy's bathroom, and that peggy also had landscapers and a cleaning woman working for her. i'm guessing you guys spent some significant time and effort running down all the people who had worked on the house? >> absolutely. >> reporter: any of that go anywhere? >> dozens of people, not a thing. >> reporter: who would want to kill peggy nadell, and why? assistant district attorney richard moran thought he had an answer for that second question. financially, she was in pretty good shape. >> very good shape. >> reporter: peggy and her husband had built quite a large nest egg. >> all in all, the estate ended up being worth about $4 million. >> reporter: wow. you've probably seen people killed for a lot less. >> a lot less. >> reporter: and who would stand to benefit? coming up -- >> i felt very early on that it

was most likely a female. >> a closer look at susanne. >> you pull the knife out. and you tell the police right away, oh, you're going to find my fingerprints on the knife. >> a few million motives for murder? >> my mother's worth high seven figures. this is not the way i wanted to get my money. peggy nadell had been

murdered in her home in suburban rockland county, new york. detectives stephen cole-hatchard and earl lorence say the team from the crime lab had shaken peggy's house to its foundation looking for a lead. >> forensically you guys got almost nothing off the scene? >> not almost nothing, you know, nothing. >> reporter: no fingerprints? >> no fingerprints. >> reporter: no dna? >> no dna. no blood, no hair. nothing. >> reporter: but the scene did tell them something. >> i felt very early on that it was most likely a female. or two females.

>> reporter: what pointed to it being women? >> the fact that there was seven or eight lacerations on peggy's skull from the statue head. >> reporter: that statue is heavy, an effective weapon in strong hands. >> my non-medical opinion is that if she was hit in the head with that statuette by a man, her head would have caved in. >> reporter: a man would have been able to swing the statuette harder? >> one or two times, at the most. >> reporter: and all of that pointed straight to peggy's daughter, susanne. not only did susanne stand to inherit half of her mother's $4 million estate, detectives thought her behavior was suspicious from the moment they arrived on the scene. >> she's saying, my fingerprints are all over the knife. my dna is all over inside the house. >> reporter: and she was telling detectives the same thing she said during the 911 call, that it was an accident. >> i think my mother fell down the stairs and stabbed herself. >> reporter: in the 911 call,

you are offering a theory of what happened. that's very unusual. >> no. i thought she fell. >> reporter: secondly, you pull the knife out and you tell the police right away, oh, you're going to find my fingerprints on the knife, which sounds like somebody who is thinking ahead to the fact that that knife's going to get dusted for fingerprints. >> sure. sure. >> reporter: would you not agree that all of that is pretty suspicious when taken together? >> maybe to them. wasn't to me. i mean, obviously they formed an opinion from the get-go. >> reporter: detectives thought this was odd as well. >> she said, listen, maybe this was a burglary. check for a large ring, a laptop and jewelry. and i called to earl, check for these three things. he called me back and said, hey, pretty much those are the only three things missing. >> i asked about jewelry, i asked about her wallet, credit cards. if they said somebody murdered her, well, why? why? was it a robbery?

>> reporter: so here you are offering theories again. >> yeah. >> reporter: then again in those first few moments, susanne started talking about peggy's money. >> one of the things she yelled out was my mother's worth high seven figures. >> reporter: and -- >> this is not the way i wanted to get my money. >> that's the exact words she used. >> reporter: this woman wants to talk her way right away. at one point, you said this is not how i wanted to get my money. >> i don't recall saying that. but if they have that on, you know, on record, you know? >> reporter: but you believe me that that's what you told police? >> yeah. >> reporter: because again you're answering a question the police haven't even asked yet. >> i guess i watch too many of those "dateline" shows in the middle of the night. >> reporter: detectives had already talked to susanne and her husband bobby on the day of the murder. questioned them for hours. you had nothing to worry about.

>> no, not at all. not at all. farthest thing from my mind is that i would be a suspect or my wife would be a suspect. >> reporter: police were feeling differently, and as their scrutiny intensified, bobby and susanne decided to hire an attorney and stop talking to the police. assistant district attorney richard moran said that slowed everything down. >> the best way to get information about the investigation would be through her. and once she stops talking to us, things take a lot longer. >> reporter: there was a point at which you and your wife stopped cooperating with police and hired an attorney. >> no. we didn't stop cooperating with the police. that's what they want you to believe. anything they wanted to know, all's they had to do was ask my attorney. >> reporter: your wife feels the same way about that? >> oh, absolutely. absolutely. she was just scared that they were gonna try and pin it on her. >> reporter: once again, susanne was right.

>> we had, we believed, probable cause to arrest susanne. we just couldn't do it because something was wrong. >> reporter: what's wrong? i mean, everything points at her. >> it would have been the easy way out to do that too early. >> reporter: sometimes you get a ground ball. >> this wasn't a ground ball. >> reporter: this would be no easy out. detectives would be going into extra innings. coming up -- the two final phone calls of peggy nadell's life. one came from a secret phone. >> these are the phones used by drug dealers, killers, cheating spouses. >> that's correct. >> could that caller be the killer? a new test with pluggable febreze. we rented this resort, hid smelly objects all over each villa and plugged in febreze. then real people were asked to stay for a long weekend. would they smell anything? the room itself was like [sniff] ahhh. feels like someone has pumped fresh oxygen into the room. on the last day we revealed everything. oooooohwoww.

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four days after peggy nadell's murder, family and friends gathered for her funeral.

for peggy's daughter susanne, it was all a blur. what's it like to process both the fact that your mom was actually murdered and that you're the suspect? >> it was horrible. horrible. i lost my mother. i lost my best friend. and now the finger is being pointed at me. >> as 80-year-old peggy nadell was laid to rest today, her daughter suzanne scaccio has hired a lawyer. >> people in the area, it's all they talked about. >> reporter: susanne's friend, darcy greenberg, was hearing it almost every day. >> there were people who said she did it. "oh, she did it." even i heard a neighbor yelled out, when are you going to arrest her for killing her mother? i mean, this is someone that probably knew us since she was a child. >> reporter: darcy was convinced susanne loved her mother and would never have hurt her. >> she was grieving. she was crying every day. she could barely get out of bed. she couldn't sleep at night.

>> reporter: peggy nadell's murder was now the biggest case ever to hit the clarkstown police department. >> we had the whole detective bureau on this and some other agencies, and i've never seen them work harder on anything in my life. >> reporter: perhaps because police couldn't talk with susanne, they stayed very close to her and her husband bobby. and very visible. >> they parked outside my house and sat. when i left, they left. when i came home, they came home. they were following my husband. >> reporter: did you think police were going to come put handcuffs on you? >> yes, i did. i was sad, and i was scared. >> reporter: police even looked into susanne's shopping habits and found something that intrigued them. susanne bought her groceries at a nearby shoprite, a big supermarket chain. in fact, she was a creature of habit, visiting there 22 times in the month prior to peggy's murder.

but on the 23rd time, the night before peggy's murder, susanne shopped at a different store, the one near her mother's house. what did she buy? >> she bought cleaning supplies, rubber gloves and some other items like that. >> reporter: had the crime scene been cleaned up? detectives didn't think so. but still found it suspicious. just before your mother was murdered, you go to the shoprite. not the one near your house. the one near your mother's house. >> mm-hmm. >> reporter: and you buy rubber gloves and cleaning supplies. >> i did. i mean, i buy cleaning supplies all the time. i have a cleaning girl. she probably needed rubber gloves. she probably needed floor cleaner. that's interesting. they knew what i bought. >> reporter: and detectives wanted to know more about who peggy might have had contact with in the hours before her murder. so they made this list of numbers they found on peggy's home phone. and as they looked at them, one stood out. it was a call from an odd area

code, and it came in at 1:17 in the morning. >> that was from what turned out to be a tracfone. they're commonly referred to as burner phones or throwaway phones. >> reporter: these are the phones used by drug dealers, killers, cheating spouses? >> exactly. >> reporter: a few minutes after that tracfone call, the alarm at peggy's front door was tripped. and at 1:23 a.m., the alarm company called. >> hello? this is the monitoring center with bullet security. >> this is peggy nadell. the code word is max, i'm sorry. >> that's okay, ma'am. >> everything's fine. >> i'm glaad glad everything's okay. we'll disregard for you. have a good night. >> reporter: it was probably the last time peggy's voice was heard by anyone except her killer. police were convinced -- still are convinced -- peggy was letting in someone that she knew. susanne?

maybe. but why would she use a tracfone to get her mom to open the door in the middle of the night? >> she wouldn't have to let me in. i have a key. and i know the -- how to work the alarm. >> reporter: right. so if you wanted to kill her, you could have waited until she went to sleep -- >> and went in. >> reporter: unlocked the door -- >> and went in. >> reporter: --disarm the alarm. >> there you go. there you go. >> reporter: police had warrants for all the family members' phones. and a few weeks later they had boxes of records to comb through. detectives analyzed susanne's first. what could you tell about susanne from her cell phone records? >> a lot. >> reporter: investigator robyn arias from the westchester county d.a.'s office specializes in phone data analysis. >> i figured out a pattern of susanne's life just based on her records. >> reporter: and on the day of peggy's murder -- >> that day was like every other day in susanne's life. there was no change for that particular day. >> reporter: and you'd expect to see a change if somebody was in the process of committing murder for the first time?

>> correct. correct. >> reporter: suggesting she's innocent? >> either she's innocent or she has another phone. but there certainly wasn't communication that indicated that something was going to happen. >> reporter: as hot as detectives were on susanne's trail, they had never stopped looking at the other members of peggy's immediate family. you talked to peggy's son jim and his wife diana right after the murder? >> yes, when they came up. >> reporter: they live in florida? >> correct. >> reporter: were they in florida at the time of the murder? >> jim was in florida. and diana said she was in d.c. >> reporter: why was she in d.c.? >> she said there was a family wedding. >> reporter: and the records backed that up. when robyn arias looked at jim's cell phone, it never left florida. diana's phone records checked out, too. where was diana's phone during that time? >> in d.c. >> reporter: that's it? didn't move. >> did not move.

the phone went to d.c., went back to florida. >> reporter: reasonable to assume that diana never left d.c.? >> absolutely. >> reporter: but you're smiling. >> there was just a break. the pattern just was off. >> reporter: diana's records were speaking to arias, and detectives were about to get a break that would shift the direction of the entire investigation. let's just say, this case was about to go south. coming up -- that secret burner phone, who bought it? who used it? get ready for a whole new circle of suspects. >> so what's going on here? how many people are involved in this? >> that's the question of the day. when "dateline" continues. get ready to show your roots...

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detectives working on peggy nadell's murder had been looking at her daughter susanne. but now they were also looking at peggy's daughter-in-law diana. diana and peggy's son jim had been married for 17 years. and while he may not have been that close to his mother, diana was always on the phone. >> my sister-in-law used to call every morning. my mother would be on my phone with me and say, oh, i gotta go. diana's calling on the other line. >> reporter: diana was a stay-at-home mom with two kids, leah and harris. peggy doted on her grandchildren

and would fly them up to new york to spend summers and holidays. detectives had already confirmed that diana's cell phone had been in washington, d.c., at the time of the murder. but when phone analyst robyn arias looked more closely at diana's calling pattern something seemed off. >> when she was in d.c. her activity was just all over the place. kind of the frenetic feel. there was definitely something going on. >> reporter: now arias looked at who diana was calling, putting names and faces to the numbers on her phone. she noticed diana suddenly seemed have a lot of new friends in washington, d.c. >> a lot of people just popped up in diana's life for a very brief moment. >> reporter: arias calls them frequent users, people diana was calling repeatedly. >> what was also interesting to me about these frequent users is that they just had such different lives.

>> reporter: diana was a suburban mom, and some of these people, well -- >> a lot of them had criminal histories living in d.c. >> reporter: remember, diana had been in d.c. for a wedding. maybe these people were, you know, those friends of the groom you have to invite? so detectives got the guest list. >> none of the high frequency callers were at the wedding. none of those people. >> reporter: and when arias looked at diana's phone records on the night of the murder, friday night into saturday morning -- >> the time of the homicide there was very little activity on her phone. like eerily quiet. >> reporter: what did that mean? diana's phone had been in d.c. that looked like a dead end. so detectives went back to that tracfone that had called peggy's house moments before her murder. the kind of phone you can buy for cash, activate from almost anywhere and then dump when you're done.

>> a lot of times that's a dead end. a lot of times. >> reporter: not this time? >> not this time. >> reporter: to figure it out, detectives began by using the tracfone number to find where the phone had been sold. and where was it purchased? >> the family dollar store in miami, florida. >> reporter: miami? >> about two miles from diana's home. >> reporter: detectives contacted the family dollar chain and got very, very lucky. family dollar was able to give them security video of someone buying a tracfone on january 23rd, just two days before peggy was murdered. is diana on the tape? >> it doesn't appear so. >> reporter: so end of the road? >> no. >> reporter: no, because the woman buying the phone was someone detectives recognized. not diana? >> definitely not diana. >> reporter: who was it? >> karen hamm-samuel. >> reporter: and how did they know who she was? >> karen hamm was somebody i had

already profiled as a person who came up frequently on diana's call records. she was a high frequency caller. >> reporter: so you got a friend of diana's buying the disposable phone that called peggy just before she was killed? >> yes. that was a big moment. >> reporter: now they knew who had bought the phone. the next step was to figure out who had turned the tracfone on. tracfones need to be activated using another phone to call an 800 number. after three weeks, detective cole-hatchard finally persuaded a tracfone manager to give him this piece of paper. >> he had circled a phone number. and it was the number that called to activate that tracfone. >> reporter: whose number was that? >> andrea benson. >> reporter: had that name surfaced before? >> yes, absolutely. >> all over diana's phone records. >> reporter: she was one of those people who had popped into diana's life when diana was in

d.c. and benson had a rap sheet. so what's going on here? how many people are involved in this? >> that's the question of the day. >> reporter: the other big question, what did diana nadell do while she was in washington, d.c.? detectives started with her arrival at reagan national airport 9:30 friday morning, the day before peggy was murdered. >> we got the video from the airport to follow her through the airport. and then follow her outside to where she got into a car. >> reporter: here's video of diana being picked up curb-side. who picks her up? >> andrea benson. >> reporter: how do you know it's andrea benson? >> it's her car, registered to her. >> reporter: you can read license plates with those cameras? >> they're pretty good. >> reporter: detectives obtained data dumps from cell phone towers in washington, d.c., that allowed them to map the travel of the cell phones as they pinged off the towers. can you follow diana's cell phone?

>> it bounced all around washington, d.c., simultaneously with andrea's. they were together the entire day. >> reporter: by late friday, the night peggy was murdered, diana's phone stopped moving and went quiet. but andrea's phone? >> we saw andrea's phone head out of the washington area and head up i-95. >> reporter: exactly the way you would drive if you were heading for peggy's house? >> right. >> reporter: along the way, the tracfone was activated. and at 1:17 a.m., it pinged a cell tower right near peggy's house. what was going on? was this murder for hire? did andrea benson drive up to new york, call peggy on the tracfone, somehow get into her house and murder her? assistant d.a. moran didn't think so. peggy would never have let a stranger like andrea benson into her house. so that had to be a friendly voice on the phone?

>> yes. >> reporter: detectives thought that voice might have belonged to diana, but they had nothing to put her on the scene, in peggy's house. at this point, is susanne off the hook? >> diana is now the higher suspect. susanne wasn't off the hook. >> reporter: they could be in this together? >> correct. >> yes. that's where it was. >> reporter: because they both benefited. >> absolutely. >> yes. >> reporter: now eight weeks into the investigation detectives still didn't know who had killed peggy nadell. with suspects in florida, d.c., and new york, detectives came up with a new strategy. and their phone expert liked it a lot. >> gutsy. like, i mean, a lot of people don't go to those lengths on a homicide case. i thought it was a brilliant strategy. >> reporter: but would it solve the case? coming up -- >> did you have anything to do with your mother's murder? >> the daughter or the daughter-in-law? >> you think i killed my mother-in-law? is that what you're telling me?

>> was one of them the killer? >> oh, god, her eyes are probably about as big as the headlights on a volkswagen beetle.

three months after the murder of her mother, susanne nadell-scaccio was still saying she was innocent and couldn't believe she was ever a suspect. you watch "dateline." >> all the time. >> reporter: sometimes, as you know, people look guilty but they're really not. are you in custody right now? >> nope. >> reporter: were you ever arrested? >> no. >> reporter: did you have anything to do with your mother's murder? >> no. >> reporter: deep into the investigation of peggy nadell's murder, the prime suspect was no longer her daughter susanne. it was her daughter-in-law diana. detectives knew that diana's friend, karen hamm-samuel, had bought the tracfone that called peggy's house just before she was murdered.

diana had told police from the beginning that she'd been in washington, d.c., to attend a wedding. but her alibi was wobbly. diana couldn't account for her time in d.c. >> she hit washington at about 9:30 and didn't reappear again until about 8:00 the next morning. >> reporter: so detectives called diana, asking her to fill in the gaps. >> i just have to confirm that you were up in washington. is there somebody i can talk to? >> what do you mean? >> we had to keep it real simple with her. listen. we just want to get you cleared. where did you spend the night? >> reporter: what did they not tell diana? detectives had a warrant and they were tapping her phone. police now sat back and listened as diana made multiple calls to people she knew in d.c. as she tried to find someone, anyone, who would say they were with her in washington at the time of peggy's murder. was she ever successful enough to find somebody to say, yes, i will say, diana, that you were

with me? >> yes, she did. yes. which was her third attempt. >> reporter: detectives heard diana tell a female friend to say diana had been at her house in d.c., but the woman seemed confused. >> so was it 9:00 in the morning or was it 9:00 at night until 6:00 in the evening? >> right. exactly. >> which one? >> 9:00 at night to 6:00 in the morning. >> okay. >> reporter: disorganized crime. >> not the most intelligent people involved, i don't believe. >> reporter: sure enough, when detectives called diana's friend, here's what she said. >> did diana stay overnight with you? >> yes. she was with me 9:00 and she didn't leave until 6:00. >> reporter: of course, detectives already knew the woman was lying, and that diana was trying to cover her tracks. but they still didn't have enough to charge diana. so they headed to miami, to speak with diana's friend who bought that tracfone, karen hamm-samuel.

they brought karen into miami police headquarters for questioning. >> all set? >> reporter: karen admitted she bought that tracfone for diana. then they asked her if diana had said anything about peggy nadell's murder. her answer blew them away. >> she did say that she was there at the mother-in-law's. >> did she tell you who stabbed her? >> no. >> reporter: prosecutor richard moran was there listening in another room. >> and that's the first time we have first-hand information that diana was in the house. >> reporter: before long, diana was in that same miami interrogation room where she recognized some familiar faces she probably wasn't pleased to see. >> you know who we are, right? >> yeah, why wouldn't i know who you are? >> okay. just making sure. >> steve and earl. >> reporter: and she knew why they were there. >> you think i killed my mother-in-law. is that what you're telling me?

>> reporter: yes, it was, and after five months, their investigation was about to end. >> you're under arrest for the murder of peggy nadell. >> i did not murder my mother-in-law. >> reporter: that same day, another team arrested andrea benson in d.c. detectives lorence and cole-hatchard were confident they had the right people in custody and that susanne was finally off the hook. she heard the news from relatives. >> they said they arrested diana for my mother's murder. and that there were other people involved in it. and i was shocked. >> reporter: what did she look like? >> oh, god. her eyes were probably about as big as the headlights on a volkswagen beetle. and her instant reaction was, i knew it. i knew it. >> reporter: susanne says her mom had been sending money to diana regularly to pay for home repairs and expenses for the kids, but she says diana wanted more. >> she wanted to live my mother's life, do all the things that she couldn't afford to do. >> reporter: and to do that all

she had to do was enlist the help of a few friend and commit a murder. >> uh-huh. >> yeah. >> reporter: detectives didn't think jim knew anything about his wife's deadly plan for his mother. and what exactly was her plan? diana had stopped talking and asked for awe lawyer. but her friend andrea benson, did talk and told d.a. richard moran the whole sordid tale. andrea said she had never met diana before and had been told by a relative to pick diana up at the airport and, as they were driving -- >> diana nadell said to her, i'm not really here to go to a wedding. i'm really here to kill my mother-in-law. >> reporter: she says this to a person she's never met before? >> yes. >> reporter: and andrea benson says, okay, i'm in? >> for $10,000. >> reporter: and right there the deal's done in that car? >> and the plan starts taking shape. >> reporter: benson said she drove the four hours up to peggy's house, and then diana

used that tracfone and called her mother-in-law. >> diana tells her, i'm here. don't you miss me? i want to come see you. >> reporter: at 1:30 in the morning and peggy lets her in. benson said she went in with diana. they were wearing hair nets and gloves to keep from leaving evidence. diana and peggy sat across from one another and talked. benson said at one point, peggy went upstairs, perhaps to call for help. she and diana followed her. then, as peggy came back down stairs -- >> that's when andrea benson started choking her. >> reporter: andrea said peggy was still alive when diana hit her mother-in-law with a metal ball and beat her with that statue head. >> andrea benson's words were, "she wouldn't die." at that point, according to andrea benson, diana nadell went into the kitchen, got a knife, came over and started stabbing peggy.

>> reporter: andrea benson pleaded guilty to first degree murder. the sentence was 20 to life. >> i need you to know just how sorry i am. >> reporter: the woman who bought the tracfone, karen hamm-samuel, was never charged with anything. diana, apparently not content to wait in jail for trial, was caught on tape trying to arrange for hit men to kill karen hamm-samuel in miami. >> tell them i said it's absolutely imperative. the one in miami he's got to get rid of. >> the one in miami. >> right. >> reporter: after that, diana also pleaded guilty to first degree murder. diana did not respond to our requests for an interview. she did speak on the day she received a sentence of 23 years to life. >> i would like to say that i'm very sorry for my actions and that i am extremely sorry for

any pain i may have caused, especially to my husband. >> reporter: susanne was there at sentencing. >> you took away a wonderful mother and grandmother. and you're going to die in hell. i hope you stay in prison until you take your last breath. enjoy prison. >> reporter: on mother's day susanne and bobby went to visit peggy's grave. >> hey mama. >> reporter: finally it was all over. >> you kind of look at life a little bit differently. you know, life is very valuable. it's precious. >> it puts things and perspective. >> reporter: you done anything special for yourself? >> i treated myself to a car. she's a fancy german lady that likes to go fast. my mother always said, spend a little. enjoy your money. you'll have mine some day. who knew that some day was going to be so soon?

that's all for this edition of "dateline." i'm lester holt. thanks for joining me. this sunday a potential po poli this sunday a potential political bombshell. word that joe biden is thinking about taking on hillary clinton. >> also, game on. it's republican debate week. >> oh, hit -- i'm going to be in the lion's, den, right? >> how will contenders deal with a wildcard like donald trump. >> i'll show up with my big boy pants on. our nbc news "wall street journal" poll with the latest clues as to who is in and who is out. i'll be joined by the other nonpolitician breaking through. retired surgeon, ben carson. we'll talk immigration, black life matters and the iran deal.

>> perhaps the worst deal in the history of america. iran deal. >> it's probably the worst deal in history of america. joini welcome to sunday. it's "meet the press." >> from nbc news washington this is "meet the press" with chuck todd. >> good morning. if you love politics and campaign, this is the show for you this morning. all this week we have been talking about one thing. the first republican presidential debate. then we have a potential political stun er. vice president joe biden is said to be taking a serious look into jumping into the race. it will end the democratic

primary. we will goat thet to that in a and what's going on in the biden world and a time that he may make the decision. >> to the man on the republican side. donald trump is going join us, and he will like what we have to say about this it morning. he is leading the pack. he is followed by jeb bush and rounding out the double leader board is ben carson at 10 percent. then you have ted cruz, rand paul and mark rubio. then there's chris christie, john and rick perry. they round out top 11. those three candidates are battling it out for two remaining spots on the thursday debate stage