a football star player, charged with murdering his girlfriend when she tried to break off their relationship for good. Opening arguments began wednesday in massachusetts. The defense is making an... See More
a football star player, charged with murdering his girlfriend when she tried to break off their relationship for good. Opening arguments began wednesday in massachusetts. The defense is making an insanity plea. And that's a tough way to go. Abc's linsey davis is here with the latest on this story. Good morning, linsey. Reporter: It was a tearful day for both sides in the courtroom. The defense was considering an insanity defense. And on wednesday, that's how they laid it all out in the opening statement. They say because of a brief psychotic disorder, fujita should not be held responsible for the crime. 20-year-old nathaniel fujita, the man prosecutors describe as a cold-blooded killer, sat in the courtroom wednesday, wiping away tears, as he heard the defense detail his future as a high school athlete, with plans to go to college. Plans that ended after prosecutors say he stabbed and strangled his girlfriend, after having a tough time with their breakup. The gaping wound, the strangulation. Every, single one of those was inflicted while lauren astley was alive. Reporter: Her grief-stricken mother became overcome with emotion during the opening statement. He wasn't able to control what he was doing. Reporter: The defense admits fujita killed the woman he loved. But said he was suffering a psychotic episode. In court, they pointed jurors to a history of schizophrenia and mental disorders in fujita's family. Saying he was battling depression during the murder two years ago, after she broke up with him. He begged her to come back in an e-mail. Please give it another sho or we'll both regret it. Nathaniel tells dr. Myers, he felt he was acting outside of his body. Reporter: But the prosecution says the murder was deliberate and premedicated, as evidenced by his attempts to cover his tracks. Hiding bloody clothes. Even putting astley's body in a marsh. And they say there was a suspicious and telling google search found on his computer. Does water erase fingerprints. I asked when you hear that, not only to think about the implications for what he did. But think about the implications for how his mind was working and what his intentions were. Reporter: Fujita pleaded not guilty to first-degree murder. He also faces assault and battery charges. If convicted, he faces life in prison without parole.
This transcript has been automatically generated and may not be 100% accurate.