Transcript for State Trooper Faces Third Trial in Family's Slaying
half hour with an extraordinary case of an indiana state trooper. David graham, was convicted twice of killing his wife and two young children. Both convictions were overturned. Now, he's on trial for a third time. Dan abrams and nancy grace will weigh in on this in a moment. First, here's linsey davis. Reporter: David will be in a courtroom this morning, defending himself on murder charges for the third time. The former indiana state trooper is charged with the shooting death of his wife, their 7-year-old son and 5-year-old daughter in their car back in 2000. A crime he's consistently denied from his first interrogation, 13 years ago. I didn't do it. I didn't do it. Reporter: He has been convicted twice. Both times he has appealed. And both times the convictions have been overturned on the grounds the court allowed inadmissible evidence about his alleged affairs, along with accusations he molested his daughter. Each time, he's been charged again. In an interview with wlky, he says he dreams about his family every night. It's a double-nightmare. I'm here for something I didn't do. Reporter: In 2005, the dna on a sweatshirt found at the crime scene, was tied to convicted arles bonet. He's been sentenced to 225 years for the deaths. Camm's lawyers say that evidence will only help their client. The judge decided the dna was admissible. And I think that that's a big deal. Reporter: This morning, camm's lawyers say, after bonet's conviction, prosecutors have been unable to admit that a mistake has been made. Prosecutors say, bonet knew camm and sold him a gun. They called dna experts to the stand last week, to suggest that camm was linked to the murders by tiny drop lets of blood on his shirt. A fine mist that could be spattered from a blood shot. But the defense argues that it was on his clothing when he pulled his son out of the car to resuscitate him. Night on and night in. And if it's because I gave my son cpr, then so be it. Reporter: Later today, the defense is expected to open its case by calling the 11 men camm said he was playing basketball with when the murders were taking place. Hoping this time there will be a fair trial. Reporter: Camm has pleaded not guilty. Meanwhile, hundreds online have signed a petition on change.Org, to free david camm. For "good morning america," linsey davis, abc news, new york.
This transcript has been automatically generated and may not be 100% accurate.