Ive referred to this case as almost being like the game of clue. You have a very small group. You know it happened in the building. What secrets were inside that warehouse . There were pry marks on her office door. Somebody moved her body. Room to room, coworker to coworker, suspect to suspect. The perpetrator could still be there. Where was her husband . Youre a suspect and so are your friends. The detective asked me if there was any trouble in their marriage. Whodunit . Sometimes desperate people do desperate things. Im lester holt, and this is dateline. Heres josh mankiewicz. Reporter 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 a local warehouse would become an anthill 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 coworkers would be dead . I just walked in our office, and i think somebody has killed somebody upstairs in our office. Okay. What makes you think somebody killed somebody . Shes laying there on the ground, and theres blood all over. Reporter impossible to believe in this tightknit workplace, where everyone knows everyone, but there was Michelle Mockbee, 42, wife and mother, face down in a pool of blood. The Sheriffs Department would launch an investigation. You know that your suspect is one of those people in the building . Thats right. Reporter probing for clues in the victims own private life. The detective asked me if there was any trouble in their marriage. Reporter eliminating suspect after suspect until there was one. He was never on our radar until we saw his truck leaving. Reporter if you give Michelle Mockbees siblings a chance to tell you about their sister, they cant say enough good things about her. I dont think theres 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. Reporter michelle carried her positive spirit into the workplace. She was head of payroll at that warehouse owned by Thermo Fisher 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. Reporter ive heard you say that pictures kind of dont do her justice. No. No. No. Michelle was much more there was a vibrantness to her. I mean, she was beautiful. Reporter it was at a Thermo FisherChristmas Party back in 1999 that dan first summoned the courage to ask her out. Youd been thinking about michelle . Oh, absolutely. Id been working on her for a year, so. Reporter 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. Reporter what went wrong . I dont know. I was totally off my game. I couldnt speak. And i thought, oh gosh, ive done screwed this up totally. This was terrible. But then i asked her out again and she said yes and reporter well, maybe you did something right. I must have. I dont know. Or she felt sorry for me, gave me another chance. I dont know. Reporter michelles family soon met him. Next thing you know, theyre seeing each other and getting pretty serious. Reporter after she came along . Oh, my gosh, world totally changed. I mean, sun got brighter. It was just a totally different world. Reporter michelle and dan married in 2001 and continued to Work Together at Thermo Fisher. 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. Reporter normal . Uhhuh. Normal. Reporter the next morning, michelle got up to go to Thermo Fisher even earlier than usual, to wrap things up before enjoying some staycation time with the family. Dan stayed at home. Hed already started his week off. She wakes me up, kisses me goodbye, says, i love you, and went to work. Reporter and that was the last you saw of her . Thats the last i saw of her. Reporter at 5 53 a. M. , a Security Camera captured michelles car as it arrived at the parking lot. She stopped by the warehouses 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 coworker, the janitor, david dooley. Ed was out on the mezzanine just part of the ways, and i was holding the door. And there was just he said, theres a dead body laying there. Reporter what did it look like . I just saw from the knees down. I didnt see the whole thing. But honestly im glad i didnt look because id never been around anything like that. It was kind of frightening for me. Reporter someone inside Thermo Fisher 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 . Theres actually industrial strength bleach there. Rubber gloves everywhere. If you needed to commit a murder, this place had it. Imagine she wont have to remember passwords. Or obsess about security. Shell log in with her smile. Hell have his very own personal assistant. And this guy wont just surf the web. Hell touch it. Scribble on it. And share it. Because these kids will grow up with windows 10. Get started today. Windows 10. A more human way to do. Tlike chicken blanketed in golden breadcrumbs and wholesome sides with her signature touches. All topped with thick, homemade gravy. 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Reporter 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. Reporter 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. A larger blood stain showing smears when lit up, as though someone had attempted a cleanup. The body itself was found in an unused mezzanine area where someone had also stashed michelles purse and a bag Holding Employee time cards. Obviously we felt like the body had been moved. Reporter putting the story together was now the job of lead investigators bruce mcvay and everett stahl. Tell me a little bit about the building where this takes place. Thermo Fisher Scientific is a company that ships medical supplies. Kind of like an amazon for medical supplies. Its a large warehouse. Reporter how large . Try the size of four football fields. Thats ulcerinducing acreage for an investigator searching for clues. But on the plus side, the warehouse was also a secure facility. Detectives say its pretty hard to get inside if youre not an employee. So you know that your suspect is one of those people in the building . Thats right. Reporter the Sheriffs Department put Thermo Fisher 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. Im sitting actually closer than you and i are sitting to the people that im interviewing. And i can see with each person i talk to, theres no blood, theres no evidence that they have been involved in anything. Reporter if its one of these people youre interviewing, theyve disguised it well . They have. Reporter dan mockbee says back at home, he started hearing about an incident at the warehouse. They werent letting people into the building. They were turning them away. Reporter dan says he tried calling his wife and other coworkers, but no one was picking up. And thats when i started getting nervous. Reporter he drove over and was escorted inside by detective stahl. Everett stahl sat me down at a table and started to ask me a few questions. And i looked at him and i said excuse me, officer. My wife works here. I really need to know that shes all right. And thats 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. Reporter while dan mockbee was being questioned, michelles family was starting to get word from the scene. I think i threw the phone down. And im just like no, no, this isnt happening. This isnt real. Reporter by dusk, the lockdown at the warehouse was lifted. I had each person walk through their day and it seemed like a normal day for everybody. Nobody stood out. Reporter and then, every Thermo Fisher 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. Reporter it didnt help that Thermo Fishers 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 dont contaminate scenes. Theres actually industrial strength bleach there. Reporter thats stronger than any you could buy in a store. Thats right. Rubber gloves everywhere, plastic bags. I mean, if you needed to commit a murder, this place has it. Reporter 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 had tried to break into it. You could tell that because . There were pry marks on her office door. Reporter what was in that office that anybody would want . Thats the mystery. You know, we talked about money, but there was very little money if any at all. Reporter the following morning, Thermo Fisher employees came back on the job, shellshocked about the death of their coworker and jittery about possibly working alongside her killer. At a command Center Meeting at the sheriffs office, detectives put their Heads Together and drew up a list of potential suspects, based on the last people to see Michelle Mockbee alive, or the first to find her dead. Ed yuska, the supervisor. He was one of the two that found the body. Reporter dave dooley, the janitor. Dave dooley was with ed yuska when the body was found. Reporter doug tungate, a temp employee, and joe siegert, a warehouse worker. Doug tungate and joe siegert were the two that saw michelle when she came in. Reporter and dan mockbee. Of course, dan mockbee because hes the husband. Reporter a short list of potential suspects for prosecutor linda tally smith. Ive referred to this case as almost being like the game of clue because you have a very small group and its a matter of accounting backwards and excluding people. Reporter so thats what faced investigators. In which room . With what weapon . And finally, who . Coming up the questions begin. Where was michelles husband dan the morning of the murder . I was sleeping. What a great alibi, right . Why did you sleep on the couch and she sleep on the bed . It made us want to take a closer look at dan. Not so long ago, on a street just around the corner. Im home. Hi dad the force was strong between father and son. You got it . What are you doing buddy . Its my ewok happy dance of course it is. Today. Hello, hello. Hey, daddy. It is passed on to a new generation. You got it . Ewok dance . Yeah. And the circle is now complete. 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Reporter as investigators worked 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 victims husband. First couple of days police werent letting you out of their sight. No. Reporter were you worried youd be put in jail . Absolutely. You know youre as innocent as can be, but theres always a possibility of something. Reporter dan was a suspect almost from the getgo. Were you guys aware of that . I was aware of it. Because the detective that came to my house asked me if there was any trouble in their marriage. To which i replied no, not at all. I not for one Second Thought that dan would be responsible ever. And i dont think any of us did. Never. Reporter but detectives werent so sure. They peppered dan with questions. Including the big one. When police asked 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 dont have to get up and go to work. I was sleeping. What a great alibi, right . Im home in bed. Its not a very good alibi, but its the only one i had. Reporter but exactly where he was sleeping that night raised a red flag for detective stahl. Dan volunteered he was downstairs on the couch. Was that a sign of trouble in the marriage . I said, well, whyd you sleep on the couch and she sleep in the bed . And he said, well, you know, typically the girls sleep with her and i get off of my shift late. By the time i get home, shes already in bed for the next day. So he had just made a habit to sleep in on the couch. It made us want to take a closer look at dan. Reporter detectives werent the only ones interested in the husband. A cadaver dog named little joe 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. Reporter detectives knew what the dog handler didnt, that the silver minivan belonged to dan mockbee. After the dogs up in the vehicle searching, he was finding nothing. There was no findings of human remains or blood. Reporter a disappointing dead end. Investigators have been in and out of this place all day long. Reporter 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. Reporter suggesting either that he wasnt guilty or that he was supremely confident he wasnt going to get caught . Thats right. Reporter while dan was feeling the heat, detectives were pulling numbers off michelles cell phone and tracking down truckers who had delivered to Thermo Fisher. And of course, stahl 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 michelles 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. Reporter the other guy at the time clock that morning was doug tungate. Doug was a temporary employee. A newcomer to Thermo Fisher and an outsider. We started looking into his past. Saw that he had a couple felonies and some alcohol issues. So we thought, this might be a good guy to look at. Reporter then there was david dooley, the janitor. He and his wife janet had cleaned at