Transcript for Massachusetts Teen's Insanity Plea in Murder Trial
For more, let's bring in "gma's" legal analyst, dan abrams. You can make the argument that anybody who commits murder is temporarily insane. The insanity defense is always hard. This is even harder because this is what they're calling a single psychotic episode. The insanity defense is easier, to some degree, when you got someone with a real documented history of mental illness, throughout his or her life. Here, you have the defense saying, this is someone with a family of people who had some mental illnes does that matter? I don't think the jury will find it relevant in this kindf case. We know that mental illness can run in families. But just to say -- can you imagine that every time someone committed a crime and someone said, there's someone in my family with mental illness. That could be every case in this country. This is a tough defense. But the prosecution has the burden to prove he was not insane. But the prosecution does have a lot of evidence, which appears to show that he not only knew what he did was wrong, but he took great lengths to cover it up. Even premedication with that google search. That's the big problem here. I think the best the defense can hope for, really, in this case, is a second-degree murder conviction. We've seen that in massachusetts before, where there's been cases where people have pled insanity. They've been charged with first-degree murder. They ended up walking away with second-degree murder. I did a bunch of research of past cases in many massachusetts on insanity. Most often it doesn't work. But the cases where it does work are so extreme. A mother who killed her children and things like that. The history of postpartum deon. Long histories, et cetera. This is a very tough defense. Bottom line, will he have to take the stand? I don't think there's a chance he takes the stand. There's no way he takes the stand. To demonstrate -- to show that you're insane. It would just be -- there's lots of defendants that do that. Not often in insanity defenses. You want the doctors to testify. I talked to him. Here's my medical opinion. Okay. Dan abrams, thanks for being here this morning.
This transcript has been automatically generated and may not be 100% accurate.