A Mt. Lebanon teenager who attacked his ex-girlfriend with a hammer before jumping in front of a trolley yesterday had apparently planned to kill her and then commit suicide, police said.

Robert DeAngelis

Sarah DeIuliis

Robert DeAngelis, 16, brought a bag containing the hammer, a knife and duct tape to a meeting with the girl, Sarah DeIuliis, 16.

County police said he attacked her with the hammer as they walked on a trail near the trolley tracks, but an off-duty county homicide detective who happened to be walking his dog nearby scared the teen off before he could kill her.

Mr. DeAngelis then jumped in front of the 42C Castle Shannon-Beechview trolley in what police believe was a suicide attempt.

He remained in critical condition today at Mercy Hospital.

Ms. DeIuliis was being treated at Children's Hospital for multiple injuries from hammer blows to the head. She was listed in fair condition.

Lt. Christopher Kearns, head of county homicide, said the two had broken up last year but that Mr. DeAngelis had some personal property belonging to Ms. DeIuliis that she wanted returned.

He agreed to return the items and they met at the school, where he asked her to walk with him for 30 minutes. They walked from the school on a paved road that becomes a dirt path near the tracks. Ms. DeIuliis assumed the bag he was carrying contained her personal items, but police said it held the hammer, knife and tape.

As the two walked, off-duty county homicide Detective Lawrence Carpico, who lives nearby, was walking his dog and saw the two ahead of him on the trail.

He didn't think anything of them and couldn't see them clearly because it was dusk. At some point after they disappeared from view, Mr. DeAngelis attacked the girl without warning, hitting her in the head with the hammer multiple times.

Police said Det. Carpico's presence saved her life.

During the attack, Mr. DeAngelis saw the detective approaching in the distance, said "someone's coming" and yanked her off the trail over an embankment.

She managed to fight him off and escape, running down the trail screaming, "Help me! Help me!"

The detective, who wasn't carrying a cell phone, took her to a nearby house and called police.

More details in tomorrow's Pittsburgh Post-Gazette.