Feb. 14, 2013— -- The lawyer for a 20-year-old Massachusetts man, charged with stabbing and strangling his ex-girlfriend, says his client killed the woman he loved because he took the breakup hard and was suffering from a psychotic episode.
Nathaniel Fujita faces life in prison without parole if he's convicted in the 2011 death of Lauren Astley. Astley's body was found July 4, 2011, in a swamp near the couple's hometown of Wayland, Mass. Fujita has pleaded not guilty to first-degree murder.
Lawyers presented opening statements Wednesday, and the defense could be laying the ground work for an insanity plea. The defense stated there is a history of schizophrenia in Fujita's family and that he was battling severe depression at the time of Astley's death, right after she broke up with him.
"Nathaniel tells doctor that he felt at that point he was acting outside of his body," defense attorney Bill Sullivan said. "He wasn't able to control what he was doing."
The defense also pointed out to jurors that Fujita begged Astley to come back in an email, writing, "Please give it another shot or we'll both regret it."
Assistant District Attorney Lisa McGovern said the killing was deliberate and premeditated, as evidenced by his alleged attempts to cover his tracks by hiding bloody clothing and hiding Astley's body in a marsh.
"Does water erase fingerprints? And I ask you, think about the implications for what he did and how his mind was working and what his intentions were," McGovern said.
The details of the killing were too much for Astley's mother, who was overwhelmed with emotion during opening statements.
"The gaping wound, the strangulation. Every single one of those were inflicted while Lauren Astley was alive," McGovern told jurors.
Fujita, then 18, was arrested shortly after Astley's body was found in the swamp by a passing bicyclist. Her throat had been slashed, leaving a gaping wound across her neck.
Astley's friends told police Fujita had an "on again, off again" relationship with her after she broke up with him in April after three years.
Police searched Fujita's home and found blood in the garage and on an exterior door handle, and traces of blood on the kitchen floor, kitchen sink and bathroom sink.
They found a pair of blood-spattered sneakers in an attic crawlspace above Fujita's room.
Police also discovered a plastic garbage bag filled with bloody water-logged clothing, including a sweatshirt with pockets containing dirt similar to that of the marshland where Astley's body had been found.
Middlesex District Attorney Gerard T. Leone said in July 2011 that this was a case of alleged teen dating violence.
"Lauren broke off the relationship. … It's a classic fatal paradigm that we see around teen dating relationships," Leone said.
ABC News' Kelly Hagan contributed to this report.