Transcript for Son becomes prime suspect in mom, brother's murders: Part 3
Reporter: Sugar Land, one of the safest cities in America has just been the scene of a horrific crime. Apparently the whole family has been shot. Reporter: Two dead, two wounded. It looks like the scene of a horrific burglary gone bad or is it? There were some things that stuck out in our minds as being odd, but nothing that we could really hang our hat on to say, this is not what it appears. Reporter: To sergeant Marshall slot the signs of burglary didn't seem quite right. The drawers being pulled out like they were and not rifled through was not typical of a burglary scene. Reporter: Nor was the fact that the only thing missing from the house was Bart's cell phone. And the burglar leaves the gun, leaves all the electronics, but takes a cell phone that we couldn't find in the scene. That was a real oddity that stuck out in everybody's mind. Reporter: It's the little details that can be the undoing of one who would devise the perfect crime. The first clues for police arise out of the whitakers' last supper. It was a celebration of Bart's announcement that he had just graduated from Sam Houston state university, but -- Bart Whitaker had not aduated from Sam Houston state. Reporter: A tiny imperfection in Bart's plot -- that became a big crack. He had not even been attending the university. He was listed in their records as a freshman on academic probation. Reporter: In sergeant slot's mind, now Bart is a person of interest. At the time you were celebrating this are you enrolled in college? I don't even remember. I don't think so. You weren't graduating from college? Certainly not. No. Reporter: Bart lying to his parents about attending school when in fact he was hanging out in a townhouse they had given him as a present. We took that information immediately and went to Kent Whitaker first with it. Reporter: Kent is blindsided by his son's lie. I realized -- how could he be so stupid? I was so mad at him. I got in a wheelchair and wheeled down to his room and I just read him the riot act about how if he had been telling the truth he would not be a suspect. Reporter: He may be a proven liar, but there's still no proof that Bart is a scheming killer. But then a police officer raises a big red flag when he remembers a call to this house two years earlier. Trish and I were awakened by a phone call from the Sugar Land police department telling us that Waco police had contacted them that Bart was on his way down here to kill us. It was something that a friend overheard Bart talking to his roommate about and they concluded that it was a misunderstanding. Reporter: Misunderstanding or not in light of the murders it is significant to sergeant slot. We've got the burglary scene that just doesn't look right. We now know that the son is not graduating from Sam Houston. Reporter: And now a prior instance of an alleged plot by Bart Whitaker to kill his family. All those little pieces set off bells and whistles in our heads -- just thinking, "We need to start looking at the son." Reporter: They warn Bart's father who refuses to believe that his son might be involved. I didn't believe it for a minute. No. 57:00 -- 7:54 P.M. Reporter: Indeed, sergeant slot was has a little more than a hunch about Bart and a lot of questions. How might he have orchestrated this? Who might he have talked to to get this done? Was this something where he was planning for a big jackpot, a payout, somehow? Officer Dubose is going to be playing the part of the suspect. Reporter: So sergeant slot returns to the whitakers' home for a vote reenactment of the murders with the two survivors, in identical arm slings. I hear "Bang!" And the next thing I realize is that I'm lying down like this. Reporter: First with Kent -- and then Bart. I got shot and I fell back into the couch and onto the floor. There were no other witnesses. So my only two sources of information, one of them is the father of the primary suspect. One of them is the primary suspect. So that was a juggling act. Reporter: Then a huge break from an mystery man who walks into the police station one night. Adam Hipp, a bank teller who went to high school with Bart. And then he dropped some bombs on me as far as, hey, Bart has contacted me before and asked me about making plans to kill his family. His father, his mother and his brother. Reporter: Adam Hipp claims Bart tried to recruit him as a shooter in an earlier murder plot. One of the plans that he laid out to me that he and Bart had discussed was the exact mirror image of the actual crime scene. Reporter: Sergeant slot decides to hatch a plot of his own. He eists Adam Hipp to trick his friend, Bart, on a trapped phone line. He told me how your mom and brother were killed and how your dad and you were shot. All that was very similar to what one of our plans was. Adam, stop saying "Our plan." Okay. Stop saying tt. All right. I was very, very, very afraid of what he had to say. Reporter: On the phone tap Bart agrees to pay Adam $20,000 in hush money. You'll pay at least $20,000? Yeah. All right, we'll work out the details. Reporter: Using a courier service he sends Hipp a $250 down payment, but then he does something brazen, signing the waybill with the name of a murderer borrowed from a Hollywood movie. Anyone could have worked for size that was his power. Reporter: Kaiser soze, played by Kevin spacey, is the criminal mastermind in the hit film the "Usual suspects." Latent fingerprints, that's what all those markers are. Every one of them on the package that was identified came back to Bart Whitaker. Reporter: Now, the police know they must warn Kent Whitaker about his son. We feel wholeheartedly that he is responsible for this and that you are living with a murderer. Reporter: But, to protect the investigation sergeant slot gives no details to Kent Whitaker. I knew they couldn't show their whole deck of cards, but they could at least tell me something if they wanted me to believe them. Kent's response to me was, "You guys are either way wrong, or my son's a monster." Reporter: Despite the warning, Kent lets Bart move back home and for the next several months Bart spends every free moment with his father, playing the perfect son, studying the bible. He appeared as if he was really listening. And I told him, "Bart, I can't read your heart. You're either zero percent responsible or a hundred percent responsible. The point is that I love you. God has allowed me to forgive everyone involved." He truly forgave the person that did this. I mean, he was the first real Christian that I'd ever met that really did what Jesus Christ told him to do. Reporter: He asked you point blank, "Did you do it, Bart?" Yeah. Reporter: And you said, "No, dad." Yeah, I did. Reporter: Even though he was going to forgive you. Yeah, but it's not that simple. I didn't want to cause that pain on me primarily and on anyone else, secondarily. So, I just was weak. I was a coward. He was lying to everybody, he was fooling everybody. He did not move out of the home. And, it was very soon after that -- Bart went missing. Reporter: Seven months after the murders, Bart's abandoned SUV is found engine running outside a Houston apartment complex. And it was crushing because up until then, there was at least one member of my family that was still here. And now he's gone. Reporter: But then a mystery man appears with evidence that would crack the case. Stay with us. And you look amazingly comfortable.
This transcript has been automatically generated and may not be 100% accurate.