Mark Presley Sr., 37, said that an officer stopped him about 3:30 p.m. and showed him a picture of the suspect. Presley, whose mother is a police officer, said he knew the man by the nickname "Fatman."
As the search continued, the Cassidy family held vigil at Einstein, attended by dozens of police officers.
"There's a wonderful spirit of solidarity," Rigali said. "Everyone is hoping. Everyone is praying. There's no way of knowing just what will happen."
Coincidentally, Jimmy Binns, a lawyer who finances sidewalk plaques honoring slain officers, was about to begin a ceremony dedicating two such memorials nearby at Limekiln Pike and Stenton Avenue when the call came in about Cassidy's shooting. The officers who had mustered for the dedication, including one officer in a kilt, ran off to respond.