Transcript for Was someone else responsible for Bonny Bakley's murder? Part 10
There had always been two theories of this case. For the prosecution it's that Robert Blake ambushed his wife and killed her. For the defense it was that somebody from Bonnie's dark past killed her. Bonnie had been scamming men for literally decades. So there were a lot of guys out there who might be pretty angry about the way that they'd been treated. So one of the guys who was mad at Bonnie was Marlon brando's son Christian and he was angry because Bonnie had told him that he had fathered her daughter Rosie but he hadn't. While the defense was preparing for the criminal trial, a woman who knew Christian brando came forward -- Dianne Mattson. The so called bombshell witness set to testify at Blake's trial about a conversation she overheard between Duffy Hambleton and Christian brando. One where brando allegedly said about Bonnie Bakley, "Someone ought to put a bullet in that bitch's head." Diane Mattson worked for Christian brando. She was his assistant. And she overheard a lot of his calls because he always used a speakerphone. She was present when Christian brando was having a phone conversation on speaker phone. They talked about the fact that Ms. Bakley had played Mr. Brando and at one point, Mr. Brando said, "Somebody ought to put a bullet through her head," and everyone agreed. He's on this phone call with a couple different guys, including a guy named Duffy. The same Duffy who accused Robert Blake of soliciting him to kill his wife. But when the police asked Christian if he knew Duffy, he denied it. Why was Christian brando denying that he knew a retired stuntman by the name of Duffy? Why would he deny it? Unless he thought it was going to incriminate him in the murder. So Blake's lawyers are very intrigued by the connection between Christian brando and Duffy. But they don't know exactly what the significance is until some guy named Brian Allan comes forward and he starts to connect the dots. In my neighborhood of willow Glen, in laurel canyon, is a cast of characters, from wealthy, behind-the-scenes movie people, to some celebrities, as well as some people that would be considered undesirable. And they did drugs, they did meth and did whatever. I realized that I had some information that I felt was very relevant to the murder. I knew a man named mark Jones who was one of these individuals that there was no question he had a drug abuse problem. Mark Jones was a transient who lived on the same street that Brian Allan lived on. He was a meth addict. He was a very handy guy and Brian used to have him do handy work around his house. In early 2001 I saw mark Jones carrying a gun that I later learned was a Walther p38 and fit the exact description of the murder weapon used against Bonnie Lee Bakley. In the weeks before Bonnie's death, Brian Allen says that he had seen that gun in mark Jones' hand several times. And he also realized that he had seen Duffy Hamilton on his block looking for mark Jones. Well, once I realized I could identify that mark Jones had possession of a weapon that looked, to me, the same as the picture, I could identify Duffy Hamilton as being part of these cast of characters that visited willow Glen. I then realized that there was more to give to the police. So months went by and I was a little surprised to not hear further from the police department, but then I got a call from a private investigator from the defense team. I was excited because I thought Brian had credibility. But I thought, "My goodness. How are we going to prove this?" So the defense starts digging and they find that other people seen a gun that looks like the murder weapon in the possession of Duffy Hambleton. And Duffy's son had seen some of his father's guns, and one of them looked exactly like the murder weapon. Duffy Hambleton was known to have a gun that looked like the murder weapon. Mark Jones was seen with a gun that looked like the murder weapon. And mark and Duffy knew Christian brando. So, when you combine all that, it's hard not to see how this evidence creates reasonable doubt. It was pieces of a puzzle that fit together. What at first seemed bizarre to me ended up being a very, very credible story that strongly suggested that either Christian brando or someone associated with Christian brando had been involved in Bonnie's murder. The defense put all of this stuff in a motion and brought it before the judge, tried to get it introduced into the criminal trial. So, you've got to bring a motion asking for permission from the court to introduce this evidence. The evidence has to be strong enough to create reasonable doubt for the court to admit it. But the judge denied our motion. Brian Allan did testify in the civil case but it didn't impact the verdict. We know that Christian brando used meth, used methamphetamine. It's certainly possible that the plan to kill Ms. Bakley, and it had so many holes in it. It was so flawed that it could have been contrived by people who were tweaking on methamphetamine. I've come to believe that Duffy hired somebody to kill her. He either did it at the instruction of Christian, or to gain favor with Christian. I'm curious about who you think killed Bonnie Bakley? I do believe that mark Jones was the shooter. Mark Jones became a different person shortly after Bonnie Lee Bakley's murder. He said he was very depressed about some things. And then mark ends up committing suicide after Bonnie's killed. The suicide happened only four weeks after the murder. Now looking back, I could see somebody who had tremendous remorse, and the fact that he committed suicide seemed to further validate that. In 2009 Christian brando died of pneumonia. A few years after that Duffy Hambleton died of natural causes. So the people who might know what happened are now dead. And in the end, we may never find out what really happened on that night.
This transcript has been automatically generated and may not be 100% accurate.