A troubled patient opened fire on a caseworker and psychiatrist in a small office at a unit of Mercy Fitzgerald Hospital in Delaware County on Thursday afternoon, police said, leading the doctor to draw his own weapon and shoot the assailant.

The confrontation left the caseworker, 53-year-old Theresa Hunt, dead and the 52-year-old psychiatrist, a veteran doctor at the hospital whom sources identified as Lee Silverman, with a graze wound to the head. The patient, Richard Plotts, was in critical condition Thursday night from three gunshot wounds.

The violence sent a shock wave through the normally quiet campus of the medical center on the border of Darby Borough and Yeadon. Police vehicles swarmed the scene and armed officers charged through the building - the Sister Marie Lenahan Wellness Center, across Lansdowne Avenue from the main hospital - to evacuate doctors, nurses, and patients waiting for routine appointments.

Authorities said they believed Silverman shot Plotts three times in the torso and arm. Silverman was expected to be released from the hospital Thursday night and recover fully.