Lauren Astley Killing: Doctor testifies that football injury could have predisposed teen to murder ex-girlfriend

(CBS/AP) WOBURN, Mass. - A forensic psychiatrist testifying for the defense in the trial of 20-year-old man accused of murdering his ex-girlfriend says the defendant was unable to control himself and may have been suffering the effects of a high school football injury when he strangled and stabbed the victim.

Pictures: Lauren Astley and Nathaniel Fujita

Nathaniel Fujita is charged with strangling and fatally stabbing Lauren Astley in July 2011. They were both 18 at the time and had just graduated from high school.

Fujita's lawyer has not disputed that his client killed Astley, but has said he did so during a brief psychotic episode.

Forensic psychiatrist Wade Myers told the Middlesex Superior Court jury on Friday that the Fujita "was unable to control what he was doing" and could have been suffering from traumatic brain injuries from playing high school football prior to the murder, CBS Boston reports.

Myers, a forensic psychiatrist at Rhode Island Hospital, told the court he had interviewed Fujita after the murder and determined Fujita had suffered from several mental problems, and didn't know the severity of what he did, the station says.

Myers said Fujita confessed to him and went through all the steps of the murder, from the strangling and stabbing to dumping Astley's body.

Fujita, Myers said, used a bungee cord to choke Astley and that "she quit moving and then he went into the house and got a knife and cut her throat."

After the murder, Myers said, Fujita smoked pot, "took a shower, went downstairs, and watched TV with his parents."

Myers said Fujita told him "he had this feeling that his mind was no longer controlling his body" and that he was "disconnected" when he murdered Astley.

The doctor told the court some of Fujita's symptoms are consistent with what happens when the brain is injured from repeated blows to the head while playing high school football, the station reports.

The hits to the head "can predispose you to having this sort of break with reality," Myers testified.

Combine that with the history of mental illness in Fujita's family - paranoia, schizophrenia, anxiety, and depression throughout every known generation - and Fujita's mind was not in control of his actions, Myers testified.

Testimony will continue Monday from another forensic psychiatrist, this one a rebuttal witness for the prosecution.

Complete coverage of Lauren Astley on Crimesider