she really shined as a mother. everything was about her kids. i can't even describe to you the feeling that came over me at that point. we were completely dumbfounded. i don't know how anyone could ever do that. >> they met on the job. >> they were an office place love story. >> and that's where she met her end. >> the blood is right by her office door. >> there's a lot of blood, a lot of trauma. >> a mom of two murdered at work. >> she wakes me up kisses me good-bye. it's the last i saw of her. >> she'd gone in extra early that morning, just a handful of co-workers in that building. was one of them her killer? >> i refer to this case as almost being like the game of clue. you have a very small group.

we know what happens within the building. >> what secrets are inside that warehouse? >> there were pry marks on her office door. somebody moved her body. >> room-to-room co-worker to co-worker, suspect to suspect. >> the perpetrator could still be there. >> where was her husband? >> you're a suspect and so are your friends. >> the detective asked me if there was any trouble in their marriage. >> who done it? >> sometimes desperate people do desperate things. >> i'm lester holt and this is "dateline." here's josh. >> they call it the early shift for a reason. it was still an hour before dawn in this small town in northern kentucky. and in a few hours the local warehouse would become an ant hill of activity as the first employees of the morning arrived. but who among them could predict

that before the first coffee break that day one of their co-workers would be dead? >> i just walked in her office and i think somebody killed somebody upstairs in her office. >> okay. what makes you think somebody killed somebody? >> she's laying there on the ground and there's blood all over. >> impossible to believe in this tight-knit workplace where everyone knows everyone. but there was michelle mockbee, 42 wife and mother facedown in a pool of blood. the sheriff's department would launch an investigation. >> you know that your suspect is one of the people in the building? >> that's right. >> probing for clues in the victim's own private life. >> the detective asked me if there was any trouble in their marriage. >> eliminating suspect after suspect until there was one. >> he was never on our radar until we saw his truck leaving. >> if you give michelle

mockbee's siblings a chance to tell you about their sister they can't say enough good things about her. >> i don't think there's enough tape to talk about michelle. she was our big sister. our role model. >> michelle was just the most amazing sister that you could ever ask for. very loving caring giving person. she would do anything for anyone. she always had a big smile and her laughter was contagious. >> michelle carried her positive spirit into the workplace. she was head of payroll at that warehouse owned by thermofisher scientific a worldwide supplier of laboratory equipment. it was also where she met her husband dan mockbee. what was she like? what drew you to her? >> michelle was funny, attractive, intelligent. >> i've heard you say pictures kind of don't do her justice. >> no no. michelle was much more -- there

was a vibrantness to her. i mean she was beautiful. >> it was at a thermofisher christmas party back in 1999 that dan first summoned the courage to ask her out. you'd been thinking about michelle? >> oh absolutely. i'd been working on her for years. >> he asked michelle to stick with him that night, and she did. and then everything went sideways. >> it was the worst date in the world. >> what went wrong? >> i don't know. i was totally off my game. i couldn't speak. and i thought, oh gosh i've done screwed this up totally. this was terrible. but then i asked her out again and she said yes. >> you did something right. >> i must have. i don't know. or she felt sorry for me and gave me another chance. i don't know. >> michelle's family soon met him. >> next thing you know they were seeing each other and getting pretty serious. >> after she came along. >> oh my gosh world just totally changed. i mean sun got brighter.

it was just a totally different world. >> michelle and dan married in 2001 and continued to work together at thermofisher. not long after along came two daughters. but even as busy parents dan and michelle always planned a date night every other monday. memorial day 2012 was no exception. how was she that night? happy? >> absolutely. >> normal? >> uh-huh. normal. >> the next morning michelle got up to go to thermofisher even earlier than usual to wrap things up before enjoying some staycation time with the family. dan stayed at home. he'd already started his week off. >> she wakes me up kisses me good-bye, says i love you. and went to work. >> that was the last you saw of her. >> last i saw of her. >> at 5:53 a.m. a security

camera captured michelle's car as it arrived at the parking lot. she stopped by the warehouse's time clock and headed upstairs to her office. about an hour later a supervisor named ed yuska noticed a big stain on the upstairs hallway carpet. he started looking around the area. with help from a co-worker, the janitor david dooley. >> ed was on the mezzanine, just part of the way. and i was holding the door. and there was just a -- he said there's a dead body laying there. >> what'd it look like? >> i just saw from the knees down. i didn't see the whole thing. but honestly i'm glad i didn't look because i never been around anything like that. it was kind of frightening for me. >> someone inside thermofisher had killed michelle mockbee. but who? and just as puzzling why? >> when we come back lockdown.

the hunt for a killer begins. >> the perpetrator could still be there? >> in this giant warehouse, a giant question. had someone carried out the perfect crime? >> there's actually industrial strength bleach there, rubber gloves everywhere. if you needed it to commit a murder, this p

- you set rules around the house, right? so set rules for your kids when they go online: don't be a cyberbully. no racy selfies. and remember everyone can see everything you post, even grandma. rules keep kids safe online. the more you know. tuesday morning after memorial day deputies from the boone county sheriff's department responded to a call of a person down at the thermo fisher warehouse. they rolled up to the front door and were directed upstairs. deputy joe gregory was with them. >> we went over to the victim assessed that she was dead. there was plastic wrapped around her head. there was plastic wrap around the back of her hands.

>> the deputies did a tactical search of the area to secure it. >> you definitely have your guns drawn because the perpetrator could still be there. >> there was no sign of anyone upstairs, but the csi team that arrived soon after found hints of what had happened a trail of blood in the hallway, laa larger bloodstain showing smears when lit up as though someone attempted a cleanup. the body itself was found in an unused mezzanine area where someone had also stashed michelle's purse and a bag holding employee time cards. >> obviously we felt like the body had been moved. >> putting the story together was now the job of lead investigators bruce mcvay and everett stall. tell me about the build wrg this takes place? >> thermo is a company that ships medical supplies kind of like an amazon for medical supplies. it's a large warehouse. >> how large?

try the size of four football fields. that is ulcer-inducing acreage for an investigator searching for clues. but on the plus side the warehouse was also a secure facility. detectives say it's pretty hard to get inside if you're not an employee. so you know that your suspect is one of those people in the building. >> that's right. >> the sheriff's department put thermofisher on lockdown. no one allowed in or out. deputies took a head count. there were 13 workers on site. detectives began interviewing them one by one. >> i'm sitting actually closer than you and i are sitting to the people i'm interviewing. and i can see with each person i talk to there's no blood, there's no evidence that they've been involved in anything. >> so if it's one of these people you're interviewing they've disguised it well. >> they have. >> dan mockby says back at home he started hearing about an incident at the warehouse sdpl they weren't letting people into the building. they were turning them away.

>> dan says he tried calling his wife and other co-workers but no one was picking up. >> and that's when i started getting nervous. >> he drove over and was escorted inside by detective stall. >> detective stall sat me down to the table and started asking me a few questions. i looked at him and i said excuse me officer, my wife works here. i really need to know that she's all right. and that's when he told me that she was deceased. >> his reaction was pretty excruciating to watch. i still had to press on. and i still had to move forward with my looking at him as a possible suspect. >> while dan mockby was being questioned michelle's family was starting to get word from the scene. >> i think i threw the phone down and i'm just like no no this isn't happening. this isn't real. >> by dusk the lockdown at the warehouse was lifted.

>> i had each person walk the other day and seemed like a normal day for everybody. nobody stood out. >> and then every thermofisher employee was sent home. as investigators wrapped up their first major sweep of the building they were puzzled. >> there was really nothing out of place in this facility. after all the searching the offices, the warehouse, there was just nothing. >> it didn't help that thermofisher shelves seemed perfectly stocked for a criminal. >> this is a company that has tyvek suits, which are what you would see in some murder investigations the detectives wearing so they don't contaminate scenes. there's actually industrial strength bleach there. >> that start eded you can buy in a store. >> rubber gloves plastic bags. if you needed it to commit a murder this place had it. >> the only sign of anything

amiss in the entire warehouse? michelle as head of payroll had a locked office. and it looked as though someone tried to break into it. you could tell that because -- >> there were pry marks on her office door. >> what was in that office that anybody would want? >> that's the mystery. you know we talked about money, but there was very little money if any at all. >> the following morning thermofisher employees came back on the job. shell shocked about the death of their co-worker. and jittery about possibly working alongside her killer. at a command center meeting at the sheriff's office detectives put their heads together and drew up a list of potential suspects based on the last people to see michelle mockby alive, or the first to find her dead. ed ed the supervisor. >> one of the two that found the

body. >> dave duly with ed when the body was found. >> a temp employee and joe seeg sieger, a warehouse worker. >> the two that saw michelle when she came in. >> and dan mockby. >> of course dan mockby because he's the husband. >> a short list of potential suspects for prosecutor linda tally smith. >> i refer to this case as almost being like the game of clue because you have a very small group. and it's a matter of accounting backwards and excludeing people. >> so that's what faced investigators, in which room with what weapon? and finally, who? >> coming up the questions begin. where was michelle's husband dan the morning of the murder? >> i was sleeping. what a great alibi right? >> i said why did you sleep on the couch and she slept on the

michelle mockbee's siblings remember her as the big sister who literally couldn't lose. >> she was the contest queen. she won every contest there was for like a two-year run. >> yeah you name it. >> flat screen tvs, tickets to everything gift cards.

>> super bowl parties. >> she loved it. made her more happy to share her winnings with other people. >> but now it was michelle's family that had lost so much. >> we were completely dumbfounded as to why anyone would want to hurt her. >> as investigators work through their list of five initial suspects one by one like the prosecutors game of clue they started at the most obvious square one, the victim's husband. >> first couple of days police weren't letting you out of their sight. >> no. >> were you worried you'd be put in jail? >> absolutely. you know you're as innocent as can be but there's always a possibility of something. >> dan was a suspect almost from the get-go. were you guys aware of that? >> i was aware of it because the detective came to my house asked me if there was any trouble in their marriage. so which i replied not at all, i not for one second thought dan would be responsible ever. i don't think any of us did

ever. >> but detectives weren't so sure. they peppered dan with questions including the big one. when police ask you where you were at the time your wife was killed -- >> i was doing what most sensible people are doing at 6:00 in the morning if they doept have to get up and go to work. i was sleeping. what a great alibi, right? i'm home in bed. it's not a very good alibi, but it's the only one i had. >> but exactly where he was sleeping that night raised a red flag for detective stall. dan volunteered he was downstairs on the couch. was that a sign of trouble in the marriage? >> i said well why did you sleep on the couch and she sleep in the bed? he said well typically the girls sleep with her. and i get off of my shift late. by the time i get home she's already in bed for the next day. so he had just made a habit to sleep on the couch. it made us want to take a closer look at dan.

>> detectives weren't the only ones interested in dan. a cadaver dog had been called in to search outside the warehouse. the dog searched two cars with no success. but then he went up to a third vehicle, a silver minivan. >> the dog did have some interest in the back of that vehicle. >> detectives knew what the dog handler didn't that the silver minivan belonged to dan mockbee. >> after the dog's up in the vehicle searching he was finding nothing. there was no findings of human remains or blood. >> a disappointing dead end. >> investigators have been in and out of this place all day long. >> but the cadaver dog was then sent over to the mockbee house to join a search in progress. one dan had consented to. >> whatever we asked of dan he was willing to do. >> suggesting either that he wasn't guilty or that he was supremely confident he wasn't going to get caught. >> that's right. >> while dan was feeling the heat detectives were pulling numbers off michelle's cell phone and tracking down truckers

who had delivered to thermofisher. and of course stall and mcvay were taking a hard look at the other four names on their initial suspect list. two men who were the last known to see michelle mockbee alive. one, a warehouse worker named joe siegert, had seemed unusually unemotional about michelle's death when he was first questioned. >> he was one of the ones that made it to the top of the list. >> joe presents himself as a loner. kind of a dry, dark sense of humor and personality. >> the other guy at the time clock that morning was doug doug tungate, a an outsider. >> we started looking into his past and saw he had a couple felonies and alcohol issues. we thought this might be a good guy to look at. then there was david dooley he was a janitor. he and his wife had cleaned at

thermofisher for over 20 years. he was one of the two to find michelle's body. >> he was interviewed the day of the homicide. and really nothing that put him to the forefront of anyone's mind. >> and last there was ed yuska. he was the supervisor who called 911 after finding michelle. >> the body is right by her office door. looks like she never got in her office. >> detective stall found out that ed yuska had some health issues. >> the thought ed could do all this to michelle drag her down the hallway and get her to the mezzanine logically to us says ed's not our guy because he physically probably couldn't have done that. >> which made detectives feel comfortable eliminating ed yuska from their suspect list. and so then there were four. now how to rule out the next one. the csi team had collected some dna from michelle's body and belongings. but detectives knew it would be months before a forensic lab

could report whether any suspect was a match. meanwhile, investigators were starting to scan through a promising new piece of evidence security video from the warehouse's parking lot. could the clue they needed be somewhere in those thousands of frames of footage? >> there it is. >> coming up -- >> it was nerve racking. >> another elimination round. this time the lie detector test. and police soon detected something was up. >> he stops himself at the door and says no no i'm not doing this.

grass fed? mhmm. i'm super into health. bottled tap water? well all bottled water is the same right? you need crystal geyser alpine spring water. made by nature, not by man. crystal geyser alpine spring water. bottled at the mountain source. now that there's foster farms simply raised, it's tougher than ever to

be a foster farms chicken. but foster farms simply raised chicken is 100 percent natural with no antibiotics. well you're an herbalist. help us to be natural. will those herbs do it? those? one grows hair, the other increases energy. gasp! do i look natural herb man? can i call you herb man? i'm trying to look natural. call me natural. you look like a steve. can i call you steve? hi steve. i'm natural. say something. why aren't you guys saying anything? introducing new simply raised chicken with no antibiotics. from foster farms. simply better. ♪ da da da da ♪ ♪ da da da da ♪ ♪ da da da da ♪ ♪ da...♪ sorry brenda. crystal geyser. bottled at the mountain source. da da da.

mother of two, michelle mockbee has been murdered at the office. she'd gone in to work earlier than usual that morning to do the payroll. an hour and a half later she was dead. police have no witnesses, no murder weapon no fingerprints. but they do have four lead suspects all co-workers. and one of them michelle's husband, dan. here >> michelle mockbee's funeral brought her brokenhearted family

some small comfort. >> i remember how many people came to the funeral. just the endless line of people coming in. in your mind you're like she touched this many people's lives. >> soon red ribbons popped up throughout town in honor of michelle. with all the community support in the world still couldn't answer the family's questions. >> i feel like we're kind of in limbo. we don't know really what to do how to move on just yet. >> we didn't know what this was all about. we didn't know if this was somebody after our family why they would be. we don't know. but we didn't know. >> early on the investigation had yielded frustratingly few clues on the four remaining lead suspects. but the detectives commander, major ben huff, kept up hope. >> i knew we could get that one little bit of lead on this investigation it would open many many doors. >> huff and his team of detectives were now hunting for that next lead by scanning through hours of security footage of the thermofisher

parking lot. >> we had several sets of eyes on this video. >> and meanwhile, stall and mcvay decided to turn up the heat on the four starting with the husband, dan. >> we asked him, would you take a polygraph for us. >> you agreed to take the polygraph? >> yes, sir. that's a scary thing. >> because if it goes wrong, all of a sudden there's a case against you. >> right. it was nerve racking. i mean i took a deep breath like this and the guy's like hold on hold on you can't do that. it's registering on the sensors. and you're like what if i took a deep breath at the wrong time? >> but dan told detectives he was eager to be put under the microscope. >> please do all this stuff so you can figure out i have nothing to do with this so you can go find whoever did this. >> dan mockbee passed the polygraph. and this time the husband didn't do it. and so then there was three. and around that time major huff

and his team spotted something they thought was unusual on the security footage. >> there it is. >> a vehicle in the parking lot, not entering but leaving around the back of the building. >> bright red, fire engine red, chevy pickup truck, two-door. that's not the normal route for any employee to take. >> detectives matched the truck to its owner, david dooley the janitor. >> dave dooley's truck is seen leaving the parking lot at 6:31 that morning. >> right after the murder? >> that's right. that's right. >> and detectives could tell from the security tape that dooley returned to the warehouse around 7:00 a.m. in time to be with ed yuska when he discovered michelle's body. detectives went to the apartment david dooley shared with his wife janet to ask where he went during that half-hour trip. >> they got there about 6:30 in the evening. and i kind of figured it would happen just to do a follow-up. >> he told me why he left the building, that he was trying to

call his wife she wouldn't answer the phone. >> my wife does take ambien to sleep and i went to check on her. >> her husband said he would often check in on her. >> he drives me crazy with did you take your medicine did you take your vitamins today? that's the kind of person he is. very sweet guy, loving guy. >> but detectives wondered did he really come home to check on his wife or to get rid of evidence? >> we started working on a search warrant for the residence and for the truck. >> you execute those search warrants and you find bloody clothing? >> no bloody clothing. >> bloody footfootprints? >> no. >> stuff taken from the crime scene that shouldn't be at his house? >> no. >> some kind of murder weapon? >> no. >> are you thinking this maybe isn't the guy? >> while they're searching the house they collected some clothing and then just some other odds and ends. but nothing that directly tied michelle mockbee to him.

>> so investigators kept looking. they asked two other suspects joe, the warehouse worker and doug the temp employee to take polygraphs. both men agreed. both passed. two more names scratched off the list. detectives had also asked david dooley to take a polygraph. >> and he said yeah i'll take one. >> but when they'd brought him down to headquarters. >> we walk him in and detective mcvay says this is our polygraph operator. and he stops himself at the door and said no no i didn't agree to this. i did not agree to this. said i'm not doing this. >> there was no asking me to do it. it was sit down and do it. i said well i want to do this with an attorney. >> dooley didn't take a polygraph at a later time either. but he says that wasn't his fault. >> i did offer to take the polygraph, they said it's too late. >> over the next few months detectives focused on dooley

significantly for detectives he was the only one they could ever identify who left the building around the time michelle mockbee was killed. after eliminating other suspects detectives now believed they'd cracked the case. in september 2012 the boone county sheriff's department arrested david dooley. >> just very glad he's behind bars. that's where he needs to be. >> as to why this happened we have no idea. >> and then there was one. >> i didn't know what to say. didn't know what to do. i was never going home. >> do you want to stop a minute? >> that's fine. i knew i was never going home. and i was upset. >> did you tell them they had the wrong guy? >> yeah i did. >> didn't do any good? >> no. >> but then the long-awaited results from the dna found at the crime scene came back from the forensic lab. it turned out david dooley was

not a match. and in the local media janet called for him to be freed. >> we've been telling everyone you know he didn't do this. nobody deserves to be accused of a crime of this magnitude without something to prove that he did it. >> but even without forensic evidence tying david dooley to the crime, prosecutor linda tally smith remained confident deciding to move forward with the case. in september 2014 david dooley went on trial for murder. >> the truth is there is no smoking gun. there is no one fingerprint. there is no eyewitness. >> so just what did the prosecutor have on david dooley? >> coming up -- >> our beliefs have always been that david dooley was in the middle of breaking into her office when she came up the steps and surprised him. >> a break-in? what was he after? and how could he have managed such a spotless escape? >> a clean pair of

- you set rules around the house, right? so set rules for your kids when they go online: don't be a cyberbully. no racy selfies. and remember everyone can see everything you post, even grandma. rules keep kids safe online. the more you know. michelle mockbee's favorite color had always been red. and since her death her family has worn red in her honor. you're all wearing your red

wristbands today. >> yeah. they say michelle ann mockbee, in our hearts 1969 to 2012. >> that was your idea? >> yeah. just a little something to remember her by. >> there was a sea of red each day as michelle's family and supporters flowed into this northern kentucky courthouse where david dooley faced trial for her murder. >> on may 29th of 2012 dan mockbee lost the love of his life. and two little girls lost their mom. at the hands of a man who couldn't even keep his story straight from one day to the next. >> prosecutor linda tally smith began by telling the jurors they wouldn't hear about any smoking gun, but they would hear david dooley's own words which she said had made him the last man standing in the detective's process of elimination. >> it was through this process

that the path kept turning back to one person the defendant david dooley. >> the prosecutor explained that at thermofisher warehouse employees used handheld scanners like this one on the job. and a scanner could help locate employees were around the time of the murder. >> we were able to create pretty much a time record of where everybody was and what they were doing at different points during the morning. >> jurors heard that almost all the employees were working on the warehouse floor, far away from the upstairs office area where michelle was killed. but where was david dooley? because he was the janitor he didn't use a scanner. which may have said the prosecutor he could have been upstairs near michelle's office during thattime. david dooley was captured on security camera that morning. >> there's a red pickup truck. >> his red truck was seen leaving the thermofisher parking

lot. >> the defendant actually left the building that day at 6:31 a.m. which was about half an hour after michelle walked into the building. >> the prosecutor filled in what she believed happened between the time michelle mockbee arrived and when david dooley left. >> she entered the warehouse, gathered the time cards from the time timeclock and headed upstairs into the offices to do her work. >> the prosecutor showed the jury a photo of fresh pry marks on michelle's office door which she said indicated an attempted break-in. michelle you'll remember had come in earlier than usual that morning. >> our belief has always been that david dooley was in the middle of breaking into her office when she came up the steps and surprised him. and ultimately she was assaulted and restrained. >> because she was a witness to a crime in progress. >> absolutely. >> the medical examiner said michelle was bludgeoned to death with something similar to an industrial packing tape gun.

but after such a violent attack why was no blood evidence ever found on david dooley? and why wasn't any of his dna left at the scene? the prosecutor argued that's because the janitor worked every day with cleaning supplies and plastic bags. perfect for removing evidence of a crime. >> at the time david dooley attacked michelle in the hallway, what did he have with him? a rolling crime scene cleanup parked with a trash bag in the middle of it. it's my personal belief that when he left that building he took with him a bag containing all of the evidence that was missing from the scene. >> but you never found any of that stuff? >> never found any of it no. >> and once dooley was back at the warehouse detectives recalled he looked noticeably fresh. >> this guy's the janitor, but he's really clean. he's got a clean pair of jeans, clean shoes. >> a cover-up so spotless only a

janitor could manage it said the prosecutor. it was only his story, she said that was a mess. >> it's very hard for a person to explain how they can't tell the same story twice. in these circumstances we had four separate statements from him. and he never told the same story twice. >> detective mcvay testified that it was what dooley didn't say in his first interview the day of the murder that made them take a hard look at him. >> at any time did he tell you he left that building? >> no he did not. >> during that first interview did he tell you he was one of the people who found michelle mockbee's body? >> no, he did not. >> mcvay says it was only at his second interview at his apartment that he first mentioned leaving work and going home. >> and i came back here. >> okay. what time did you come back here? >> 6:30. i couldn't get ahold of my wife and came home to make sure she was okay. >> but detective stall says dooley's wife janet told stall something different. >> i asked her specifically if dave ever came home that

morning. and she said no. >> in a later set of his and hers interviews janet said david did come home to change a pair of red pants. >> he had to come home and grab a pair of pants. >> it sounds like an alibi except david dooley adamantly denied doing that. >> i never said that. >> however, jurors heard that a warehouse co-worker erer also remembered dooley talking to him the morning of the murder about ripped pants. >> he had a conversation in which he said he had to go home and change his clothes because he had ripped his pants. >> while the prosecutor had focused on david dooley's own words and that suspicious drive away from the murder scene, next the defense was about to point out to the jury all the hard evidence investigators didn't have on david dooley. >> dna evidence murder weapon

blood evidence. >> and the defense would ask who else would have more of a reason to want michelle dead. >> coming up -- >> did you have anything to do with the death of michelle mockbee? >> no i did not. i did not kill her. >> mystery dna, a possible intruder, a husband on the stand. so many questions. and, a final bombshell from the prosecutor. >> sometimes desperate people dond a lot of time online around here. but with all this speed from xfinity, it's all good. hey, why don't we do some homework for a change? gary, you too. dad...work stuff. yes! lovin' the new design! konichiwa hirosan. five minutes... all this speed is very empowering. check out the new hardware. with the fastest internet available, xfinity is perfect for people who need to get a lot done at home. and now you can go even faster. we've just increased the speeds

on two of our most popular plans.

jurors had listened for 12 days as prosecutors laid out a

very circumstantial case against david dooley. so circumstantial that his defense attorneys chris roach and tom pugh say they sometimes wondered why dooley was even on trial. >> we're trying to figure out exactly what they were saying linked david to this murder at all. the one thing that we could see was bad for him at that point was just he went home that day. >> in court prosecutors had focused on that trip home. and according to detectives that dooley never mentioned the trip in his first statement to them. but the defense said because that interview wasn't recorded what can anyone really know about what was or wasn't said? >> without actually having his interview now we're going based on one detective's notes saying he didn't go home that day. >> david dooley says he knows what he told them. >> i did tell them i went home. i was always very adamant about that. >> dooley never testified in front of the jury but he did

talk to "dateline" about the case against him. and his story that differed from his wife's. you say you went home to check on your wife. they talk to your wife and she says he never came home. then later in a separate interview she says he came home because he tore his pants and he came home to change his pants. so what's the truth? and why can't you and your wife agree on the same story? >> we do agree that i came home. i have never heard an interview where she said i did not come home. this was his testimony. >> the detective? >> yes. as far as i'm concerned if it's not the truth, it cannot be factually proved. >> did you go home to change your pant sns. >> no i did not. >> why would your wife say you did? >> i do not know. we've talked about that a couple of times. the only thing we can come up with is she didn't hear me properly. >> janet says she's been diagnosed deaf in one ear. on the day of the murder she says she only saw a pair of ripped pants in the house and thought david said that's why he

came home. >> i told them what i thought i heard him say. so a person that cannot hear they put things together themselves through their eyes. and i did. >> in court the defense sought to set the record straight for the jury. >> dave didn't change his clothes. and dave didn't change his story. >> as for that co-worker who also had a story about dooley telling him he ripped his pants? >> why did he wait five to seven days later onto all of a sudden recall oh yeah david said this. >> and the defense pulls the million-dollar question to the jury. who would want michelle mockbee dead? >> is money motive? for whom? >> the jurors heard that the mockbees had around $25,000 in credit card debt. dan said he had no idea. >> i never took care of the finances at all. she wanted to do it.

and i was more than happy to let her. >> the defense then asked dan about the insurance payout he received after his wife's death. >> do you recall the amount of the payment? >> $700,000. something like that. >> we're not saying that we know or believe whether or not dan mockbee killed his wife. but it's about reasonable doubt for our client david dooley. >> but more significant to the defense was the unknown dna found at the crime scene. dna was found on michelle's body or on her belongings in at least five different places. >> we heard testimony there were many unknown dna profiles. one of these unknown profiles have been the killer? >> the defense also disputed that thermofisher was a secure facility. and noted that something had set off the warehouse alarm system just three days before the murder. you think that's significant? >> yeah.

yeah it's significant. that means that someone could have gained access to thermofisher. >> after both sides had presented their cases, it was time for closing arguments. now each side would have its last opportunity to speak to the jury. the defense went first. >> no one could think of any reason to kill michelle mockbee. so what motive would david dooley have to kill michelle mockbee? >> but it was only after the defense had wrapped up its closing that the prosecutor gave her answer to that question laying out her theory of motive for the first time. >> i would suggest to you that the evidence is right in that stack of stuff there. you have time cards, you havin voices all kept in michelle's office. >> you think the motive was the time cards? >> yeah. i believe michelle had actually discovered the fact that he had actually been triple dipping by clocking himself in clocking his wife in and getting paid hourly to do a job that they

were already being paid a monthly salary to do. >> that feels like a thin motive. >> sometimes desperate people do desperate things. >> defense attorneys never had a chance to challenge that theory in court. but they say there was zero evidence presented by the prosecution to prove it. >> the thing about it is if there was some evidence they would have put it in there. >> what about the theory that you were double dipping your pay? >> it is not true. >> you were not double dipping your pay or triple dipping or stealing? >> no we were not. >> but the jury would have to render its decision based only on what was presented in court. after deliberating for some 16 hours over two days word came. there was a verdict. >> we the jury, find the defendant david dooley guilty of murder under instruction number five. >> guilty of the murder of michelle mockbee. the jury foreperson told "dateline" in the end david and janet's own statements which

jurors felt were inconsistent helped them reach their verdict. david dooley was sentenced to life in prison. he says he regrets not taking the stand. and has filed for appeal. did you have anything to do with the death of michelle mockbee? >> no i did not. i did not kill her. >> you know getting convictions reversed on appeal is a long shot? >> but when you're innocent it does happen. and it will happen. just like it always has. >> you think you'll be a free man one day? >> yes, i do. >> michelle's family believes strongly that the jury got it right though the aftermath is bittersweet. >> nothing's going to bring michelle back. there is no justice that is good enough. >> now their focus moving forward is on giving love and support to dan and the girls.

what do your daughters say about this? >> neither one of them want to talk about it to this day because they're just too sad. >> dan is hoping the two young women he's raising will carry the spirit of the one he lost. >> we've talked about mom and things she liked to do. she just exuded personality and fun and happiness. and that's what michelle was. >> that's all for now. i'm lester holt. thanks for joining us. next at 11:00, a critical cool to keep you safe in a radiation disaster you. >> want it there, you want it there quickly. >> how long it will take to reach the bay area. >> plus the dangerous new high exploding onto the party scene.

when we win b/c it's all on us... ==jess/cont vo== nbc bay area news starts now. >> tomorrow is going to be ban asas when we win. because it's all on us. >> right now at 11:00, the warrior fans on the brink of history. businesses prepping as the city braces for potential championship celebration. geepg, everyone. i'm jessica aguirre. >> it's tricky for any city preparing for a parade and celebrations. tomorrow night's game is in cleveland, but a sellout crowd