when buttons are pushed, people get angry. in my brain they're at the top of the stairs and they're struggling. i eventually heard a lot of details i didn't really want to hear. i had nightmares for months. >> reporter: a young mother dead, at the bottom of the stairs. >> this isn't what it's made out to be. >> things in this crime scene were moved before we got here. >> things aren't adding up. >> reporter: her body, bloody and covered in paint. >> one of the most odd scenarios that i could ever dream of. >> it was on the front of her body. it was around her body. it was on her arms. >> it's another means of covering up. >> reporter: who was covering up, and why? was this murder about money? >> anna marie was a big spender.

she owed other people money. >> reporter: or love? >> it was a relationship of extremes -- hot, cold -- wild, calm. >> you know, love is crazy. >> reporter: and caught in the middle, the person she loved most. >> everything was about brianna. everything. >> reporter: would a body covered in paint help a killer cover up a murder? >> almost 24 years of doing this job, i've never seen a perfect crime. >> reporter: a history-making case with a verdict that stunned everyone. >> god, where art thou? >> reporter: i'm lester holt and this is "dateline." here's dennis murphy with at the bottom of the stairs. >> reporter: the phone calls of the "are you sitting down kind" started buzzing on a dank, rainy evening in western massachusetts. it was march 29th, 2010. >> i said, "oh, my god. you know, you gotta be kidding me." >> reporter: the news was heartbreaking. incomprehensible. >> i couldn't be. it couldn't be true. it's just wrong. >> reporter: word spread from family members to friends. >> how did you find out something awful had happened?

>> i was at my desk at work and my wife at the time called me and said, "sit down." >> i heard there was an accident. that's what i heard. >> reporter: annamarie cochrane rintala and to friends and family was dead. she was only 37. married. a mother. and now her body lay at the bottom of the basement stairs. >> it was devastating. >> reporter: if ever there was a woman who took life in big gulps, it was annamarie cochrane rintala. even as a little girl growing up amidst a big irish-italian family in springfield, mass, she'd loved the limelight. pasquale martin is her uncle. >> the first time i had seen her take the stage and sing "mambo italiano," it just knocked me out. >> reporter: not afraid of the spotlight, huh? >> nah, she loved it. >> reporter: she could belt it out to the rafters but was she any good? her friends t.j. donahue and mary petrone are diplomatic.

>> she thought so. >> she was -- oh. no, i -- she could carry a tune. but she thought she was much better than she actually was. >> it didn't really matter because she -- >> it didn't. >> she had the charisma -- >> yeah. >> -- to kind of pull off anything. >> reporter: t.j. became tight with ann in high school and one day, the two of them pulled off a ferris bueller spectacular, skipping school, road-tripping all the way from springfield to new york city in her mother's car. they were 16. t.j., that's a hooky day. >> i know. i think we're try -- >> reporter: that's not just going to the movies or hanging out. >> no, no, no. it was a big deal. however, we ended up getting caught 'cause ann left the -- ticket for the george washington bridge in the car. she was impulsive like that. >> reporter: when she settled into a career, the bright lights she went for were atop an ambulance. she became a paramedic. that was another thing about ann, she wasn't all look-at-me in the spotlight. she wanted to serve, too.

so, i'm not surprised that she ended up working with people. >> reporter: did she like the adrenaline of it? running hot with the blue lights going? >> i would say yes. >> i would say yes, 100%. yeah, who she was. >> reporter: it was under those flashing lights, back in 2002, that ann met another paramedic named cara rintala -- and fell for her. like ann, cara was compassionate. but in other ways, she was ann's opposite. if everything about ann was larger than life, everything about cara was contained, even cautious. sandy montagna is cara's mom. carl montagna, her stepdad. >> she had a plan. always had a plan. was very conscious of where she was headed in life. >> reporter: after a couple of years together, ann moved into cara's house in the western mass town of granby and they decided to adopt. >> this is a real step. i mean, being a couple together and moving in your furniture is different than, "we are going to raise a child together." you know, this

>> and so, i don't think it was looked upon lightly. i remember that cara wanted a 2 or 3-year-old boy. and they ended up with a six-day-old girl. >> reporter: weeks after brianna came into their lives, ann and cara quietly went to the courthouse and got hitched. >> she and ann are -- are defining their relationship at a very prominent time in american -- >> oh, yeah. >> sexual politics, and especially in the state of massachusetts, which is taking massachusetts, which is taking the lead on same-sex relationships. all of a sudden, couples are getting married in the courthouse. >> well. i don't think that cara would've gotten married -- just because she didn't feel like a piece of paper was that important. but ann really wanted to have the same last name as brianna. >> reporter: in the years that followed, there were happy times with brianna -- the little girl who meant the world to them. a day before ann died, they attended service at the reverend lori souder's serene church and everyone seemed so contented,

fresh from a vacation. >> when i stand at the pulpit and i look around and it's like they're here. they've returned. i knew they were away in florida and they were full of light. >> reporter: when suzanne cordes saw them, after the service, they struck her as a couple who had it all together. >> they were showing me pictures of a trip they had gone on. and they seemed, like, perfectly happy. >> reporter: so how to explain the horror at the bottom of the stairs? poor ann lying stiff as a mannequin. and something beyond strange, there was paint all over the place, on the body and beside it. >> reporter: what had happened to ann? a terrible accident? or something much darker? when we return -- >> there's a large amount of blood and there's several lacerations to the head. >> reporter: and, left behind, a daughter with one less mother, an

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hless because it's perfect. you'busted tail.rd. and impressed the boss. maybe, it's time to be your own. transform your career with strayer university's mba program today. let's get it, america. >> reporter: on that rainy march afternoon when ann died, cara rintala was running errands with her 2-year-old daughter. they got home around 7:00 p.m., saw the basement light on. and inside, cara peered down the basement stairs. her wife's bare feet were lying on the floor. cara grabbed her daughter and raced to her neighbor's. then home again. >> my neighbor just came over and she told me to call 911.

she was pretty distraught. >> reporter: she was. when sergeant gary poehler of the granby police department arrived at the rintala house about 7:20, he heard cara before he saw her. >> it was, "she's dead, i can't believe she's dead." crying, lots of crying. >> reporter: nothing prepared sergeant poehler for what he saw when he went down those basement stairs. >> there was cara rintala, sitting on the floor with a female, looked like a female party across her lap. later found out it was anne marie. she had her eyes open. her arms were out, extended like this. >> reporter: there was blood. smeared and streaked. and something truly weird. >> paint all over the place. all over this female that she had across her lap. >> reporter: within minutes, more first responders arrived. some were paramedics who knew cara and ann, had worked with them. they helpe h

took her upstairs to wash. massachusetts state trooper jamie magarian, the lead investigator, studied the scene. let it talk to him. any obvious injuries to the victim here? are we talking about stab wounds, bullets holes -- >> no. no. >> reporter: lacerations, abrasions? >> there's a large amount of blood and there's several lacerations to the -- the head. >> reporter: it seemed like the body had been there for a while. >> i touched the deceased for the first time, with rigor mortis setting in, i thought, how long that body had been on that floor. >> reporter: there was an open paint bucket at the scene. and paint -- light-colored paint -- everywhere. >> the paint, to me, is fresh paint. it's wet. there was a thin layer of paint on the deceased that appeared to be dry in some spots, but then there was other paint on the deceased that was still wet and a large amount of paint on the floor that was wet. >> reporter: did this look like the case of somebody who had taken a bad fall? and somehow ends up knocking into the paint can and causing

configuration of where the deceased was in relation to the stairs and where the paint bucket was, you couldn't fall directly down those stairs and tip that paint over. >> reporter: other things spoke to the trooper. items on the basement floor with blood under them. the trooper took out a pencil and gingerly lifted a laundry basket. there was blood beneath it. what'd that tell you? >> it tells me that, you know, things in this crime scene were moved before we got here. >> reporter: police videoed the scene. that night, a shattered cara rintala called family members, breaking the dreadful news. and then she went to the granby police department for an interview. it was almost midnight when detective lieutenant robin whitney hit record, turning the clock back to 8:30 that same morning when ann got home from her overnight shift. >> we were talking. she made me coffee. >> reporter: playtime with a noisy brianna followed. then lunch. and after, a request from ann, a paramedic, remember, who was trying to nap before another

overnight shift. >> she's like, can you just go to the mall or whatever. >> reporter: cara and brianna left the house about 3:00 p.m., she told detective lieutenant whitney, the good-bye to ann -- just matter-of-fact. >> that's all i can think of, you know? is the little good-bye greeting. "see you later," you know? and here we are. >> reporter: mother and daughter had a busy outing, shopping for socks at the mall, going to mcdonalds to grab food for brianna and then, a change of heart, going to a burger king instead for mac and cheese. >> and haven't been able to get ahold of ann. we've been texting, we've been calling. >> reporter: then home. brianna spotted ann's body first. >> and bri's like, "mama down there?" and i -- well, i didn't know what to do. i was just -- i wanted to scream. i wanted to run down there. but i didn't want to freak brianna out. i didn't know. so i ran out the house. >> reporter: ran to her neighbor's with her daughter. en

moving. not moving. not moving. >> did you turn her over? >> yeah. yeah. so i did. i did. >> yeah? >> i wanted to turn her over, you know, like -- you know? and she was cold. >> reporter: and then, she said, she sat with her arms around her wife's body. >> this is nothing like i've ever been trained for. i've never -- >> i know. >> experienced anything like this. honestly, training? i could -- i know now, i couldn't work on a loved one. >> reporter: but what about the paint? >> where'd the paint come from? paint's been down there for months. >> reporter: it looked as though ann fell down those stairs. so what happened down there? was it an accident? or something more sinister? >> you can't rule anything out. >> reporter: but trooper magarian was determined to find out. little did he know how long it would take.

for suspicion. >> you have wet paint. we know items are moved in the basement. those are all flags that come up. >> reporter: and a person of interest. >> there was an emotional affair at a minimum. >> reporter: when "dateline" continues.

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>> you have wet paint. we know items are moved in the basement. those are all flags that come up. >> reporter: and days later, the medical examiner would confirm those suspicions. the cause of death was strangulation. ann was a homicide victim. pasquale martin is her uncle. >> rep

it? >> of course, it would. but to have somebody rob somebody from you, steal, take, murder, just rip them from the world, you know, hard to fathom, hard to swallow. >> reporter: now investigators were looking into a murder. they began a deep dive into ann's life. prosecutors steve gagne and jen suhl of the district attorney's office joined the team. they learned that ann cochrane rintala's life could often be grand opera. and her relationships could be complicated. take the thing she had going with a fellow paramedic named mark oleksak. >> mark oleksak was a very close friend of anamarie. they started as co-workers then became very, very close friends. >> reporter: the two were on intimate texting terms. that last morning, ann texted mark asking him to go to best buy for her. "can you please go sat at 6a for me. i will get there about 825a with a coffee. and a big kiss." mark, at the time, is a married man. >> he was a married man, two

>> i think very clearly there was an emotional affair at a minimum that happened between mark and ann. >> reporter: investigators didn't think the two had a sexual relationship, but it was clear they had a financial thing going. mark opened his line of credit to ann. no small thing where ann was concerned, because her big passion was shopping. ann's friends t.j. donahue and mary petrone. >> i do know that ann loves jewelry. she loves nice things. >> gadgets, right? >> gadgets, cameras. i mean in high school, she was that same kind of person. so, she loved to spend money. >> reporter: and sometimes the spending got ahead of her. mark learned that. >> he co-signed, i think it was three total credit cards with her, one of which had racked up about a $7,000 balance at one point. >> reporter: and another thing. after ann's death, when investigators asked mark what he was doing the day of the murder, he wasn't straight with the facts. not at the beginning. first, he said he was at home that day. later, he changed his account, said he'd actually been shopping, then shared a meal

>> reporter: that must make your nose twitch when a guy doesn't give you the straight out story. >> i agree. it's going to raise the suspicions a little bit. >> reporter: even though mark oleksak's story changed, investigators accepted it. he had receipts for his purchases. and the final texts between the two seemed to affirm they were close until the end, mark promising ann a "big long kiss cause i love you." >> even the morning of the murder they were very lovey-dovey on text messages that particular morning. >> reporter: and you don't think -- >> but he also -- >> reporter: the financial -- the outstanding debt gets you there? >> no. there was nothing to suggest that mark was upset about that outstanding debt. she was paying him back for that debt. >> reporter: but investigators were looking at another possible. a police officer named carla daniele. ann had dated her before she met cara. but it turns out, that wasn't the last time the two would be an item. in 2009, ann and cara were going through a rough patch. they separated for a few months

and ann went back to carla. >> and from carla's perspective, perhaps the love of her life was coming back to her. >> reporter: and some more credit cards and more spending here, huh? >> yes. and as with ann's friend, mark, ann started to rack up a little bit a debt on carla's behalf. >> reporter: racked up about $10,000 on carla's card. but then in late 2009, ann abruptly returned to cara and their daughter. carla was history. she was dumped, huh? >> she was blindsided. carla said she was devastated. she took it very hard. >> reporter: so was carla in the basement that march day? here's a person who was romantically involved, emotionally tied to her, is dumped and there are money issues between them. >> she was on the short list of persons of interest or suspects, call them what you will. >> reporter: but carla told investigators she went to her gym, a 30-minute drive from the rintala home, about 3:00 p.m. the afternoon of the murder. said she went out for a long

then left the gym at 7:00 p.m. investigators located security images that supported her account. is carla's alibi rock solid? or does it have a window for foul play? >> i would say it's pretty rock solid unless she had access to a helicopter. >> reporter: that left investigators with one remaining suspect, the one who'd topped their list since the night of the murder. the person who knew ann best, who loved her, and who fought with her -- cara. because as sunny as these two seemed in public, sometimes behind closed doors they went after one another. as cara admitted in her police interview. >> we'd argue and it would get physical, absolutely. and i'm no angel. but i can honestly say it was definitely back and forth, you know what i mean? >> mm-hmm. >> reporter: their troubles were well-documented. in 2008, ann had cara arrested for assault. she dropped the charges. but a year later, each woman filed for divorce, with ann asking for custody of daughter brianna. within weeks, each applied for a

restraining order against the other. brianna was caught in the middle. >> when the other would try to pull brianna away that was problematic. >> reporter: so the child was the glue that held them together, but it was -- >> mm-hmm. >> reporter: also the source of a lot of this friction, huh? >> correct. >> reporter: money was an issue, as it so often was with ann. cara was frugal. ann, free-spending. and between them, a growing pile of debt. >> their finances were now starting to become commingled. and ann's debt and ann's spending problems were part -- starting to become a problem for cara, too. >> reporter: but in early 2010, they were together, working hard on their marriage. in february, they went on a cruise. then came march 29th. the bottom of the stairs. and only one person, investigators believed, had the opportunity, and motive, to kill that day. >> all the evidence kept leading us right back to barton street, where that homicide occurred. >> reporter: but they knew they had a circumstantial case. >>

evidence which conclusively said, "cara rintala killed her wife." >> reporter: still, they decided to go for it. 18 months after ann's death, in october, 2011, cara rintala, living in rhode island by then with her daughter, was arrested and charged with ann's murder. cara's mom got a call to come pick up brianna. >> and brianna, when i got there she said, "why was mommy crying?" i had to think fast. i said, "because she's a great paramedic and they needed her for an important job." and so, they took her. and that's why she's crying because she's not going to get to see you right away. >> reporter: so it was that cara rintala would have the dubious distinction of being the first woman in massachusetts history to be charged with the murder of her lawfully wedded wife. an extraordinary journey through the criminal justice system was just beginning. >> reporter: coming up -- little evidence, but some odd behavior when cara saw her wife

at the bottom of the stairs. >> cara's a paramedic. what does she do? does she rush down there, "oh, my god, ann! are you okay?" no. >> reporter: and what was cara throwing away in this parking lot? machines don't have emotions. but the rare few can inspire them. ♪ with a naturally aspirated 5-liter v8 engine, and a 10-speed direct-shift transmission. the first-ever lexus lc. experience amazing. what do you have there? p3 it's meat, cheese and nuts. i keep my protein interesting. oh yea, me too. i have cheese and uh these herbs. p3 snacks. the more interesting way to get your protein.

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>> reporter: prosecutors knew when cara rintala was arrested in late 2011 for murder, they had a mighty challenge on their hands. and so it proved. the trial opened in early 2013. and it ended, three weeks later, with a hung jury. >> breaking news, a northampton jury has failed to come to a unanimous verdict. >> reporter: a year later, in 2014, trial number two. same thing happened, incredible as it seems. another hung jury. ann's family, convinced that cara was the killer, was frustrated, wondering why a jury couldn't get there. >> i trusted her with my niece's life. and she took it. >> reporter: soon afte c

was bonded out of jail, free to spend precious time with brianna. meantime, prosecutors wrestled with the facts. they had a circumstantial case. no smoking gun. no eyewitnesses. would they go again? you really do have to step back and say, "are we going to do this a third time?" >> we did. the first thing we did was we consulted with ann's family they were onboard. and that i think gave us the strength and the courage to step up again. >> reporter: so it was set. cara rintala would be tried a third time for the murder of her wife ann. but first, cara had a heart-to-heart talk with brianna, now 9 years old. >> she told her a lot. and she says -- >> that some people -- >> mom, i already knew. >> she says, "some people think i did something bad, something terrible. but i just want you to know that it's not true." >> reporter: in september, 2016, trial number three opened here at hampshire superior court in northampton, mass. prosecutors steve gagne and jen suhl returned with a streamlined argument.

this trap of being responsive to the defense and we decided let's play offense. >> reporter: in trial number two, they'd put the possibles, mark oleksak and carla daniele, on the stand, only to knock them down as viable suspects. perhaps, they reasoned, they had confused jurors. so this time, they were gone. and now they focused on cara, and the helpless victim who fell down those stairs. the wife who was strangled, they said, for as long as four minutes, until she died. >> her last precious breaths that she took on this earth were taken with the defendant's hands around her neck. squeezing, squeezing, squeezing, and squeezing more, until every last breath of her was gone. >> reporter: prosecutors laid out a timeline for murder that began with a nasty fight by text the night before. ann, working the overnight, jealous that cara was home alone with a male friend. she lashed out, "i hate the relationship we have. no one does that.

no respect." cara's response, "okay, you being over the top and crazy." >> it really is, in our mind, a fuse being lit, something that continues into the next day. >> reporter: the next morning, the last of her life, ann, a phoneaholic, called or texted friends and family members 58 times. >> i want show you one final entry. >> reporter: the final call to her beloved aunt nancy was placed at 12:21 p.m. then, uncharacteristically, ann went silent. >> do you remember if she left a voicemail on that occasion? >> no, ma'am. >> you did not speak to annamarie that day, is that correct? >> no, i didn't. >> reporter: the timing of that last call was important, prosecutors argued, because they theorized cara murdered her wife soon after, then spent hours cleaning and covering up. remember that afternoon of errands? prosecutors showed security video of cara and brianna shopping and argued it was part of the cover-up.

>> she leaves the house around 3:00 p.m., according to her, but she doesn't pop up on surveillance video until 5:00 p.m. that evening at the holyoke mall. >> suddenly starts using her debit card left and right to make miniscule little purchases. >> reporter: what was going on, do you think? >> she was trying to be seen. she was trying to be elsewhere. in short, she was creating a digital alibi for herself. >> we are still driving. love you. bye. >> reporter: an audio alibi, too. prosecutors played voicemails. all play-acting, they said. >> on our way to burger king. call. please, please, please. >> the whole reason she's out is to try to let her get some sleep. that just didn't add up. >> reporter: and now, a pretty big deal. these cleaning rags. >> can you just hold that up for the jury to see? >> reporter: prosecutors said cara used them to mop up. one contained a woman's dna. which the prosecution's expert said could have been ann's. but it was what cara did with the rags, that prosecutors wanted to talk about. that's her vehicle on surveillance video leaving mcdonald's. s

truck in a pouring rainstorm, walk over to the farthest-most trash receptacle at mcdonald's, dispose of three cleaning rags and drive away. >> reporter: they also highlighted cara's odd behavior after she saw ann's feet at the bottom of the stairs. cara's a paramedic. this is her wife. what does she do? does she rush down there, "oh, my god, ann! are you okay?" no. >> reporter: she raced to the neighbors, prosecutors told jurors. then ran back home with one more job to do. >> before the paramedics and the police arrive, she makes one final desperate attempt at covering up. she picks up that container of paint. she pours that paint. >> reporter: but instead of masking the evidence, the prosecutors said, that paint pointed to cara's guilt. >> the stiff body was clearly not something that had just happened. the paint being on the floor was something that had just happened. >> reporter: and now prosecutors played their ace. they called a new witness to

heard from in previous trials. >> do you solemnly swear to -- >> reporter: engineer david guillianelli. he really did watch paint dry, conducting dozens of lab experiments. >> were you able to form an opinion as to that time frame when the paint might have hit the floor? >> yes. >> and what is your opinion? >> within approximately 30 minutes of the time the first responders arrived. >> reporter: the final coat of a slap-dash cover-up. but motivation. why did by most accounts, the more sensible one of the two, turn on her fiery partner? prosecutors said the seeds were planted some ten months earlier. and they played an audiotape from a contentious court hearing to prove it. >> i'm not going to play games with this. >> reporter: it was may, 2009. ann and cara had each filed those restraining orders against the other. a district court judge heard them sniping at each other and erupted, threatening to have dcf, the department of children and families, take custody of brianna. >> if i seth

court, i'll be on the phone to dcf so fast, they'll be here before you get out the door. >> reporter: it was a turning point. because of the judge's warning, each woman now knew that one wrong move could cost them custody of the daughter they adored. so the prosecutors' theory of what happened on march 29th. there was a violent fight and ann went down those stairs. whether she was pushed or not, they couldn't say. what mattered, they told jurors, was what happened at the bottom of the stairs. >> the defendant had to make a choice. call for help. likely face criminal charges. lose her home. lose her daughter. lose her livelihood. or, on the other hand, make ann go away. and she made her choice. >> reporter: now it was over to cara's defense team. they'd managed to avoid conviction twice.

could they do it a third time? >> reporter: coming up, from witness to the prosecution, to a key witness for the defense. >> is he going to say, "investigator, you ran a shabby case here. you didn't secure the scene." >> yeah. he just needs one nugget of doubt. >> reporter: when "dateline" continues. which didn't get me to my goal. lowers my a1c better than the leading branded injectable. the one i used to take. victoza® lowers blood sugar in three ways. and while it isn't for weight loss, victoza® may help you lose some weight. non-insulin victoza® comes in a pen and is taken once a day. (announcer) victoza® is not recommended as the first medication to treat diabetes and is not for people with type 1 diabetes or diabetic ketoacidosis. do not take victoza® if you have a personal or family history of medullary thyroid cancer,

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♪ take it down take it down >> reporter: cara rintala's family and friends agree on a couple of things. first, that cara is a great mom. ♪ do i do i >> reporter: and if she has to sing herself silly to entertain her daughter -- well, she's in. ♪ my beautiful daughter brianna ♪ >> reporter: the second thing friends say is this, cara did not murder her wife. not in a million years. suzanne cordes, who first met cara at church, says she knows her like a sister. >> cara would never do that. the woman that i know, the devoted, loyal, compassionate, caring, thoughtful, faithful mother that i know would never ever do that to her wife. >> reporter: when the third trial commenced, friends and family sat behind cara in court, practically willing a victory. attorney david hoose opened, as he had in trials one and two, for the defense. >> this case, ladies and

bias. a mindset that caused the investigators and the experts to focus on one theory, one person and to ignore everything that didn't fit, sometimes going to frankly ridiculous extremes to do so. >> reporter: that one theory was, of course, that cara murdered her wife in the course of one final terrible fight. the mindset, attorney hoose said, was there from the very beginning, in the neighbor's 911 call. listen to the dispatcher's words. >> she said the other one was down in the basement and but she didn't say -- >> maybe it's a domestic. >> reporter: and, attorney hoose said, remember this question from detective lieutenant whitney, a scant seven minutes into the lengthy police interview on the night ann died. >> all right, so let's back up a bit. you have a history of domestic violence with anna, right? >> reporter: even that powerful voice from court. >> if i see that come into this court.

insisted that noisy scolding from the judge was anything but the trigger for murder. did that scare them? >> yeah, absolutely. that was when they did a turnaround and they decided they had to, you know, grow up -- >> reporter: straighten up for the daughter? >> yeah, pretty much. >> reporter: and by march, 2010, although prosecutors hadn't acknowledged it, the defense told jurors the couple had put their troubles behind them. >> they focus on a nine-month period, which was undeniably a rocky patch in this relationship. a nine-month period out of a nine year relationship. >> reporter: but what about that angry volley of text messages the night before the murder? the fuss over cara's male friend's visit? attorney hoose hit that hard. >> the commonwealth wants you to believe, that this was the battle of all battles and the fight that ended everything. well, you know, you've got to have some proof of that.

and i'll tell you why. you can look at these texts and once again, cara is the calm one. ann is the one who goes from zero to 60 in about three seconds. >> reporter: and by the next morning, the defense attorney said, ann was going her breezy way, promising her buddy mark that "big kiss" in a text. >> not a word about fighting with cara. not a word even like, "gee, things aren't too good around here right now. cara and i had a big fight." nothing like that. >> reporter: then to that afternoon of errands. and, from cara's side, an explanation for the trip to the trash can at mcdonald's. >> because that's what they did. they had to pay for their trash bags in granby. so they were dumping their trash wherever and whenever they could. >> reporter: the defense brought in its own expert to knock down the prosecutors' argumenat

>> i have no idea what the source of the dna on that rag is. >> reporter: but perhaps the most damaging evidence against cara was the paint. attorney hoose went after the prosecution's paint guy on cross. his weapon of choice? sarcasm. >> you're the first guy as far as you know who has ever testified about reading wrinkles and cracks in paints, is that correct? >> that i'm aware of. >> your honor, can we please change the tone here? >> reporter: the defense attorney had to persuade jurors that cara hadn't poured the paint. he accused the paint expert of buying into the first responders' observation that the paint was wet. >> first responders -- these are people you've never met, correct? you don't know how much training they have or if they've even seen a bucket of paint before, correct? yet you're ready to credit their subjective impression that the paint was either wet or shiny, correct?

>> correct. >> reporter: finally, the defense called, of all people, state trooper jamie magarian. in the first two trials the lead investigator had been a heavyweight witness for the prosecution. not this time. he was vital to the defense theory of a keystone cops investigation. >> is he going to say, "investigator, you ran a shabby case here. you didn't secure the scene." >> certainly. >> reporter: "there were tests you didn't run. there were things to be known. you're relying on this junk science of how paint dries." >> yeah, that's his job. he just needs one nugget of doubt. >> reporter: in pursuit of that nugget, the defense attorney grilled the investigator about the two people of interest. first, mark oleksak. remember, he'd changed his alibi. but what motive could he have for murder? well maybe this -- ann, the drama queen, had angered him when she left her wife for her old girlfriend. >> he described that he had a big fallout with ann. is that correct? >> yes.

>> and the fallout was when he became aware that ann was seeing an old girlfriend. correct? >> yes. >> an old girlfriend named carla daniele. correct? >> correct. >> reporter: a wisp of doubt, perhaps, dating back to ann and cara's separation. and what about carla? remember, she said she'd been miles away at the gym and out running on the day of the murder. security images seemed to support her account. but the defense produced a bank record dated the day of ann's death from an atm closer to the crime scene than the gym. >> did you ever ask her about how that could have happened if she was running in east longmeadow? >> i don't know that -- i've never asked her that. >> reporter: the name of the game for criminal defense lawyers is creating reasonable doubt. had the defense finally gotten there with all 12? >> reporter: coming up, an anxious wait. >> did you think this was going to go down in flames again? >> i did. yeah, absolutely. >> reporter: then -- the verdict. >> i'm sti r

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>> reporter: after two hung juries, the prosecutors in cara rintala's third murder trial weren't taking any chances. this time, they added a lesser charge -- manslaughter. did it mean di

wanted to salvage half a loaf out of this thing? >> we thought there's no harm in giving this jury yet another option of a verdict of guilty. >> reporter: cara's family and friends didn't buy that. >> we had asked for manslaughter in the first trial and they said, "absolutely not. no, no way." well, all of a sudden, you turn the tables? because they want this to end. >> and cara's take on that was, "i don't want that because that means i did it. and i didn't." >> reporter: deliberations began on a tuesday morning. day one passed in silence. no questions from the jury. day two, the same. day three. again. some began to speculate about another hung jury. t.j. donahue and mary petrone. did you think this was going to go down in flames again? >> i did. you know, what can be different this time? >> reporter: team cara tried to keep her spirits up. >> there was a double rainbow and i took a picture of it and i sent i

there's a double rainbow tonight." >> reporter: finally on day four, late in the afternoon, news. >> the court officer who knows us very well, he sort of just came in very gently and he says, "hey folks -- we have a verdict." and immediately upon that moment, hearing that, my heart starts racing. >> i walked back with cara to the courthouse and she was breathing, you know, really deep breathing. i said, "cara, it's going to be okay." >> the defendant would please rise -- >> reporter: inside the court, a verdict read by the foreman, off camera. >> she's guilty of murder in the first degree. >> reporter: guilty of murder one. the most severe charge. cara broke down.

her friends and family stunned. >> you need to remain silent. >> it's, like, you can't believe it. there's nothing. nothing to point to cara. how could this possibly be the worst possible outcome? how? >> reporter: afterwards, reverend lori souder, cara's pastor, friend, and firm defender, lamented. brianna has clearly lost her other mother now, in a sense? >> yes. god, where art thou? >> reporter: ann's family was also stunned. but pleased. >> murder one -- i'm still reeling on that one. it's what we wanted for the last two trials. >> it was a surprise but really, just an affirmation of everything we had done. >> the possibility that it could have been anyone else and adhere to the timeline -- >> reporter: so what was the jury's thinking? they say they kept running into inconsistencies, beginning with cara's account of discovering ann's body. why didn't she rush to help her? >> she was a paramedic.

so to see your loved one at the bottom of the stairs and she could've easily have gone down there and started cpr and saved her. she didn't know that she was dead at that time. >> reporter: then, that paint. lacey, do you agree there're some time problems between when you believe the time of death is and this paint still being wet? >> oh, absolutely. yeah. >> reporter: what do you make of this? >> i really -- i almost wanted her to admit to spilling the paint, just to make sense out of it because without her spilling the paint, it just didn't make any sense. >> reporter: finally, the matter of premeditation. was this a planned act? >> cara had her hands around annmarie's neck for up to four minutes. so that's a long time to reflect and restrain yourself. and nellie did this great thing where she just timed four minutes. and you sit there and think about your hands around this person's -- >> reporter: i can elect to not strangle you at this point.

it was a real long time. >> reporter: they were ready for the final vote. >> and it was clearly 12 yeses -- of guilty. >> to come to the conclusion that, you know, cara was the bad guy, was a really hard one for us to reach. >> we didn't want it, but that's what it was. >> reporter: for ann's family and friends, it's a time to be grateful for justice. to remember the irrepressible spirit they lost, the woman who loved life and the spotlight. >> she would love this. >> she would love to be interviewed. oh, my goodness. >> she's watching right now. like, "come on!" "say something funny." >> reporter: cara rintala got the mandated sentence -- life without parole. she is appealing. each week, her parents take brianna, the child they are now raising, to see her mother in a massachusetts prison. >> when cara was crying, she says, "mommy, it's okay. you don't have to cry." >> "you gotta be strong." >> "you gotta be strong," that's what she said.

>> reporter: the kid, that little girl, the other victim in this tragedy, the child who, in an instant, lost two mothers at the foot of the basement stairs. >> reporter: that's all for this edition of "dateline." don't miss "sunday night with megyn kelly," this sunday at 7:00 p.m./6:00 central. and, of course, i'll see you each weeknight for "nbc nightly news." i'm lester holt. for all of us at nbc news, good night. at ikea, we believe that everything you need should be within reach. in an affordable dream kitchen that works as hard as you do. save up to 15% at the ikea kitchen event. so, when it's your turnt to do the shopping and you need to get...

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