Updated

Mary Schaab's only daughter was fatally shot 17 months ago, so she understood the horror and pain of losing a child, even before a Pennsylvania state trooper knocked at her door late Thursday to tell her the same thing had happened again -- this time to her son.

Up until then, Schaab had not been especially worried as she watched the television news coverage that day about a gunman who killed one person and shot several others at the Pittsburgh psychiatric hospital where Michael Schaab worked.

"We sat and watched the news for hours and not even thinking (he might be a victim) because he worked on another floor, an upper floor," Mary Schaab said, referring to news accounts of the shooting on the first floor lobby of the Western Psychiatric Institute and Clinic.

Police now believe Michael Schaab was returning from a lunch break and just happened to be in the lobby when police say John Shick, 30, opened fire.

University of Pittsburgh police shot and killed Shick, but not before the gunman wounded six others.

"A trooper came by and told us, about 10 or 11 last night," the Greensburg mother said Friday.

Her 25-year-old son, who lived in Edgewood, had indeed been the lone dead victim of the shooting she had followed on TV all day.

Nancy Schaab, her 26-year-old daughter, was fatally shot Oct. 23, 2010, at the residence she shared with a man named Jordan Just. Although her death was just as upsetting to her mother, authorities say Nancy Schaab was involved in the violence that ended her life.

Police say Just shot Nancy Schaab during an argument over heroin. They say he suffered a concussion, broken nose, and a small stab wound to his arm before the fatal shooting. Just pleaded guilty to voluntary manslaughter last June and is currently serving a six- to 15-year sentence at the State Correctional Institution-Cresson in central Pennsylvania.

The killing of Mary Schaab's son is less clear-cut, especially since Pittsburgh police have yet to determine the gunman's motive.

Michael Schaab had worked at the clinic since getting a bachelor's degree in psychology from the University of Pittsburgh. His mother was too distraught after learning of her son's death to recall the year he graduated. The clinic is part of the University of Pittsburgh Medical Center, a hospital network that dominates health care in western Pennsylvania.

"He was just going back to school to get his masters, in occupational therapy. He just got engaged. We were just planning his wedding," she sobbed. "March 2013."

Schaab said that her son loved his job and that his patients in the clinic's geriatric unit and their families thought highly of him.

"I have letters from patients' families that just raved about him, about how good he was to their spouses or mother or father," Schaab said. "If you say anything, just say he was the best person in the whole world."