Dr. Cyril H. Wecht today may cast doubt on the most incendiary testimony in the trial of a Mt. Lebanon teen charged with trying to kill his ex-girlfriend with a hammer. He is expected to testify that based on the girl's injuries, she doesn't appear to have been struck with a hammer.

Sarah DeIuliis, 18, is the only viable witness to the attack on Oct. 31, 2007, in which she suffered a mild traumatic brain injury, a laceration to the head and a fractured eye socket. Immediately afterward, her former boyfriend and Mt. Lebanon High School classmate Robertino DeAngelis threw himself in front of a moving light rail train and said he does not remember any of it. He suffered life-threatening injuries and has undergone more than 30 surgeries, according to his mother's testimony yesterday.

The teen with untamed curls dressed in a blue suit and tie listened intently yesterday as two doctors testified about the victim's injuries.

Ms. DeIuliis, now a freshman in college, testified Monday that several months after their breakup, she met with Mr. DeAngelis -- at his insistence -- to return each other's belongings. As the two walked along a wooded path near their high school on Halloween, she lost sight of him and felt a blow to the back of her head. She testified she was hit multiple times. She told Common Pleas Judge Kim Berkeley Clark, who is hearing the case in juvenile court, that when she asked him what he had hit her with Mr. DeAngelis said "a hammer." She then grabbed a red 31/2-pound claw hammer and still had it in her hand when she ran into an off-duty county homicide detective who was walking his dog in the area.

Defense attorney Patrick Thomassey said he did not deny his client's involvement in the attack, but he considered it "a fight between a couple of kids."

A childhood friend of the defendant's testified yesterday that Mr. DeAngelis often carried a hammer with him in his backpack because he came to the friend's house to help out with construction projects. Mr. DeAngelis, 17, also had a roll of duct tape and a knife among his belongings.

The defendant's mother, Diana DeAngelis, yesterday portrayed the victim as shrill, antagonistic and a threat to her son's well-being. She testified that far from pursuing Sarah DeIuliis, her son tried to stay away from her. He had switched out of her homeroom after the breakup.

"Robertino wasn't going to school because he was afraid of Sarah," said Mrs. DeAngelis, an attorney who passed off all her clients to help take care of her son after his injuries. "He was always avoiding her," she said.

She said several weeks prior to the altercation, Ms. DeIuliis showed up at the DeAngelis house screaming at her son to return several erotic Japanese Manga comic books and a sketchbook. He wanted Ms. DeIuliis to give him back his knife.

Mrs. DeAngelis later made copies of text messages on her son's phone sent by the young woman that she thought sounded threatening.

Dr. Wecht, the former Allegheny County coroner, will be called today as a defense witness. He has conducted about 17,000 autopsies, by his own estimate. These include hundreds on victims of blunt force trauma akin to a hammer attack. He is expected to review the victim's records and say that the blows are not consistent with a hammer.

Assistant District Attorney Meghan Black may call the current Medical Examiner Karl Williams as a rebuttal witness.

Hammer or no hammer, it will be Judge Clark's discretion to determine whether the defendant intended to kill the victim.

Even if the judge determines that the victim was not struck with a hammer, she may still find that Mr. DeAngelis set out to kill Ms. DeIuliis. He could still be adjudicated delinquent, the juvenile court equivalent of a finding of guilty, on that charge and the remaining charges, two counts of aggravated assault and unlawful restraint. Or she may rule that if there was no hammer, he couldn't have meant such serious harm.