Defense Rests in Trial Over Girl’s Prom-Night Slaying : Courts: Psychiatrist speculates on why many of the teen-age witnesses lied or gave misleading information to police.

The defense rested Monday in the murder trial of Paul M. Crowder, with a psychiatrist speculating as to why many of the teen-age witnesses lied or provided misleading information to officers who were investigating the post-prom shooting death of Berlyn F. Cosman.

Dr. Gloria Keyes, a forensic psychiatrist at Atascadero State Hospital, testified that there were numerous reasons why young people, confronted by a traumatic event like the shooting of a friend, might react in that way.

It might be, she said, that they suffered from hysterical amnesia, or that they were simply lying to protect a friend.

Under cross-examination by Deputy Dist. Atty. Christopher J. Evans, Keyes said that while she would not classify the young people’s conduct as sociopathic, it might indicate underdeveloped consciences.

Another witness, defense investigator Sue Sarkis, denied that she had manipulated an interview with Gena Phillips, one of the teen-agers who attended the party. Earlier in the trial, Phillips testified during the interview, the investigator told her she was mistaken when she said she had seen Cosman exchanging angry words with Crowder in the doorway of one of the hotel rooms.

Sarkis testified that, in response to a question from Phillips and as a courtesy to her, Sarkis explained that none of the other teen-agers who attended the party had said that Cosman was in the doorway.

Cosman, of La Crescenta in Los Angeles County, a 17-year-old basketball star for Crescenta Valley High School, was shot in the head on June 1, 1991, as she slept in a darkened room of the Crown-Sterling Suites Hotel in Anaheim.

Crowder, 19, who has pleaded not guilty to a murder charge, testified earlier in the trial that he fired the .357 magnum pistol accidently as he stumbled into the room after a long night of drinking.

Numerous other teen-agers who took the witness stand--some as young as 15 and few of whom actually attended the prom--said they went to the all-night party without their parents’ knowledge. They said that there was considerable alcohol and drug use in the three hotel rooms occupied by party-goers, and that at least four guns were brought to Anaheim for no particular reason.

Many of the young witnesses acknowledged that in the hours and days after the shooting they lied, dissembled, misled or left out information in interviews with police.

Closing arguments are slated for today, when the jury is expected to begin deliberations.