the young man in massachusetts on trial for murdering his high school sweetheart. Fate of 20-year-old nathaniel fujita lies with the jury. Was he temporarily insane when he killed his girlfriend.... See More
the young man in massachusetts on trial for murdering his high school sweetheart. Fate of 20-year-old nathaniel fujita lies with the jury. Was he temporarily insane when he killed his girlfriend. Linsey davis starts us off. Reporter: Highly charged, impassioned closing arguments on both sides tuesday. At one point during the prosecution's closing argument the lawyer actually dropped to her knees with a bungee cord allegedly used to strangle lauren around her throat. She then asked the jury to think about how brutally she was murdered. There's no question that nathaniel fujita killed his 18-year-old high school sweetheart. This morning jurors are charged with determining whether he was temporarily insane when he did it. There is no psychosis fairy who magically sprinkled a temporary dose of sigh coast season this defendant. Reporter: In their closing argument the prosecution tried to convince jurors the former football and track star was sane and his actions were not only deliberate but premeditated. Even telling lauren to park out of sight the night of her murder. The time for blaming football, the time for blaming marijuana, the time for blaming the victim is over. Reporter: But the defense argues fujita just 18 at the time of the murder was suffering a psychotic episode when he beat, strangled and slashed his girlfriend and then dumped her body in a marsh in july of 2011. Several weeks after they graduated from high school and not long after she'd broken up with him. Apply the law to those facts in a manner that is not swayed by emotion, by sympathy or anger. Reporter: Last week, the defense called on a psychiatrist who testified fujita suffered from a major depressive episode leading up to the murder followed by a brief psychotic episode and cognitive disorder from football injuries. But the prosecution countered with another psychiatrist who testified she believed fujita was exaggerating how depressed he was. Dr. Fife, in your opinion what did drive the defendant to kill lauren astley? I think the primary motivator was rage. Reporter: Enraged or insane? Now up to a jury to decide. The psychological profile is key. If the jury determines that the murder was premeditated, fujita faces life in prison without parole but if he's found not guilty because of lack of criminal responsibility aka he was insane at the time he could be committed to a mental health facility and never do any time behind bars. George? Okay, linsey, thanks. More from "gma" legal analyst dan abrams. The prosecutor didn't think much of the brief psychotic defense. Tough defense. They presented two witnesses, a psychiatrist and a relative, and even though the prosecution still has the burden to say he was not insa this is a very tough thing to get a jury to accept. I think the best shot that the defense has here is second degree murder which would mean that the jurors don't believe the prosecutors proved premeditation or extreme atrocity or cruelty. Now, even that's going to be tough to get second degree murder here. But the notion that a jury would acquit based on a brief psychotic episode would be almost unheard of. Might they be reluctant to send a 20-year-old to life without parole. They might and why he has a shot at second degree murder, life in prison with the opportunity for parole after something like 15 years. Sympathy for the defendant is the best he can hope for, i think, in this case, although, look, the defense is going for it all here and hoping that he somehow gets ac okay, dan abrams, thanks very much.
This transcript has been automatically generated and may not be 100% accurate.