Reporter: Months go by, and those nomadic electricians in the room next door have long since departed Texas. But now, convinced that Greg Fleniken was killed by a bullet fired from the neighboring... See More
Reporter: Months go by, and those nomadic electricians in the room next door have long since departed Texas. But now, convinced that Greg Fleniken was killed by a bullet fired from the neighboring hotel room where those electricians from Wisconsin were staying, detective Scott apple and private eye ken Brennan travel there for a new round of interviews. They meet up at a local police department with electrician Tim Steinmetz, who once again appears courteous and curious. So what happened to this guy? Did you guys ever find out the whole point? Reporter: Time and time again, they ask him what he remembers. You didn't hear anything? You don't know anything that went on? Absolutely no idea? No idea. Reporter: Steinmetz sticks to his original statement, that he, lance Mueller, and Trent pasano did nothing out of the ordinary that night. No mention of any gunshots. And Steinmetz doesn't just tell that story, he swears to it in writing. I said, "Let's get a notary as well and have it notarized so it looks even that much more official." Do you swear everything this statement is the truth, the whole truth, so help you god? Yes. Reporter: But just when he thought he was off the hook, investigators pull him back in. It was their plan all along. Is that it? Hang on a second. Oh. It was until you signed that statement. Now, you got a problem. Okay. You don't think that we know the story, that we don't know what the hell went on here? Of course, we know. What are you, a moron? You just made a -- false police report, that's why. You want to go to jail for that? Tim, we know what happened. We know everything that happened down there. And I realize you're trying to be noble and protect a friend, but you're about to get your whole family in a bind, and it's not worth it. And after, the guy started thinking about that and he, and he says, "Okay, I'll tell you the truth." No, I don't want to go to jail. Well then, tell us what happened. Reporter: Steinmetz begins to reveal the pieces of the puzzle, explaining how the evening was fueled by alcohol, Steinmetz and fellow electrician lance Mueller entering the hotel with that beer. They're later joined by electrician Trent pasano, and the heavy drinking begins next door in room 349. It was an accident. It really was. Reporter: It turns out Mueller has a handgun in his truck and at some point, for some reason, Steinmetz says the third electrician, Trent pasano, goes to fetch it. We were in the room, and Trent brought lance's freaking gun up there. And lance was Around with that gun. And he went and loaded it, pulled the freaking trigger, and the gun went off. Reporter: Later that day, they track down the third electrician, and Trent pasano corroborates the story. Listen as he explains how he nearly became the victim in this case, saying the bullet just missed him. And he goes, bam. And I went like this. Son of a bitch. And I looked, and there was a hole, and it was smoking. Reporter: It turns out that private eye was right, the bullet slicing through the wall in room 349 and heading directly for Fleniken, striking him in the groin area and shooting straight up to his heart, all while he was sitting there watching "Iron man 2," all of that internal damage caused by a single shot from that 9-millimeter handgun. Afterward, Mueller quickly packing up the gun and returning it to his truck, exiting the hotel with a bag then returning moments later without it. And never telling anyone, those electricians try to cover both their tracks and that bullet hole. Reporter: And what was it they put in there? Toothpaste. Reporter: They put toothpaste in the hole? Mm-hmm. Reporter: Thinking no one would ever notice? Exactly. Reporter: No one went to check on Greg. No one alerted the front desk. Never bothered to knock, never bothered to put their ear to the door, heard any moaning or anything, nothing. Reporter: The next day, even when they see a body carried out on a gurney from the room next door, they say nothing. This is not an accident, you know? This is a murder. He pulled that freaking trigger. I sat right there and watched him do it. Reporter: The only man missing at confession central was the shooter himself. Watch as apple and Brennan have Steinmetz call the gunman. Steinmetz urges Mueller to turn himself in. I said they probably are going to come and get your ass. I don't, I don't know. But now that they know the truth and everything, you should probably try to make some kind of effort, you know? Reporter: Listen in as Mueller realizes they figured it out. Oh . I mean, they're going to come and get me. Reporter: He pleads no contest to a charge of manslaughter, a judge sentencing him to 10 years in prison. The others are not charged. I don't think he did the right thing. I don't think anybody did the right thing. Reporter: Inside that courthouse, Susie Fleniken watching on, saying it all could have been avoided had they simply checked on her husband that night. Had he simply come forward, this would have been a completely different, quote, "Accident." She was disgusted with their behavior. She felt like they basically disregarded him as a human being. Reporter: Susie did not want to go on camera, trying to preserve that quiet life she and her husband once shared. But she did tell us of that private eye she hired, "I would trust him with my life." What did Susie say to you? You know, she was determined that, you know, that there would be justice, that she would find out who killed her husband. And she was successfully able to do that.
This transcript has been automatically generated and may not be 100% accurate.