Michigan 'Mad Scientist' Trial

Michigan man accused in 23 highway shootings says demons haunted him and he's not a killer.
3:00 | 01/28/14

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Transcript for Michigan 'Mad Scientist' Trial
We'll begin with a Michigan man accused of 23 highway shootings taking the stand in his own defense after terrorizing a community. As his victims now tell their emotional stories in court. ABC's gio Benitez has the story. Reporter: Hey, robin. The shooter said demons haunted him. He's not a killer and was simply afraid. The question right now will jurors believe him during deliberations today? They were the horrifying shootings on Michigan's popular freeway, the I-96. Drivers terrorized. Their cars shot up. I'm okay. There was a gunshot that went through the backseat of my car. Reporter: Now this morning for the first time we're hearing from the confessed shooter himself. Reilly Castile taking the stand saying he thought drivers were part of a government conspiracy against him. To my way of thinking at the time, it was to get rid of the demons, so to speak. It was those thoughts, the fear, the anxiety. Reporter: The 44-year-old is charged with terrorism, assault with intent to murder and firearms charges for the October 2012 shootings but during two hours of testimony Monday, he said he never intended to terrorize or kill anyone. I didn't have any thoughts that I wanted to murder someone. Reporter: After being fired from his job as a scientist at the university of Michigan, Castile says he believed his phone calls were being monitored and that government helicopters were watching him. They would hover above the rooftop and what seemed like really an attack on a house. Reporter: Miraculously, in the 23 shootings, only one person was hurt. Seen here on surveillance video limping into a gas station for help. Another driver says the bullet missed her by a millisecond and that Castile was laughing when he shot at her car. I just started hysterically crying because where I could see the bullet was, it was just so close to where I was sitting in my vehicle and I knew that could have been me. Reporter: Castile has pleaded 23409 guilty to the terrorism and assault charges. If convicted, he could face life in prison. And Castile has already pleaded no contest to some of the shootings and on Thursday he'll be sentenced for assault with intent to commit great bodily harm less than murder and firearms charges but insists he is mentally ill, robin? All right, gio, we'll bring in Dan Abrams to weigh in. Mental illness as a defense. Yeah, but he's in a tough spot because under Michigan law, it's all or nothing meaning you either plead the insanity defense and you say, I didn't understand right from wrong or you go for not guilty. He seems to be trying to go for something in between, which is to say I'm not going to go for the insanity defense because I understood what I was doing was wrong but I still was mentally ill. That's not under the law a defense in Michigan. Used to be, something called di americanished capacity where you seek to get a lesser conviction. Not a valid defense under the law at this point. Hoping for the sympathy of the jury. Would the jury understand that, just what you said? Yeah, I mean, look, jurors are human, right, and I think -- it's actually kind of smart, meaning if he pled insanity here, he would have lost. There's no way that he would have gotten a jury I think to find him not guilty by reason of insanity saying he didn't understand right from wrong so considering that it's very clear he was the shooter, his best shot is to get up there on the stand, by the way, very unusual for someone to testify about their own mental illness, get up on the witness stand, testify about his own mental illness and hope that maybe some of these jurors will feel sorry for him in some way, shape or form. We'll see what happens. Thankfully, again, no one was seriously injured and mental illness, it is something to be taken seriously. Absolutely. Just knowing -- Keep in mind in his guilty plea in that other county, all it means is he's going to get help in prison. He'll get mental assistance. He's not going to get a lower assistance but by pleading no contest but mentally ill he'll get some treatment. Good point there. Thanks, Dan. Now to Alec Baldwin.

This transcript has been automatically generated and may not be 100% accurate.

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