The psychiatrist, Dr. Lee Silverman, was grazed in the temple during the gunfight in his office Thursday afternoon with patient Richard Plotts, Delaware County District Attorney Jack Whelan said.
"We do believe that there were some issues between the doctor and the patient, but whether or not he actually feared him is unclear," Whelan said.
Plotts, 49, was hospitalized in critical condition. He was expected to be arraigned on murder charges Friday at his hospital bedside in Philadelphia, said Emily Harris, a spokeswoman for the district attorney's office.
The prosecutor identified the caseworker killed at Mercy Fitzgerald Hospital as Theresa Hunt, 53, of Philadelphia. Hunt had accompanied Plotts to an appointment with Silverman at a psychiatric crisis center adjacent to the hospital in Darby, just southwest of Philadelphia, authorities said.
"When the caseworker was shot, (Silverman) crouched down behind the desk to avoid him being shot," Whelan said. "He was able to reach for his weapon, and realizing it was a life or death situation, was able to engage the defendant in the exchange of gunfire."
A struggle ensued and spilled out into the hallway, Whelan said. Another doctor and a caseworker jumped in to help Silverman and secure Plotts' weapon, he said.
The motive for the shooting remained unclear.
Whelan said Plotts, of Upper Darby, might have had issues with the doctor over his treatment plan. It is not known, however, if that is why Silverman was armed.
Silverman was recuperating at home Friday. His wife said he did not want to discuss the shooting, and she also declined to comment.
A spokeswoman for the Mercy Health System said the hospital has a policy barring anyone except on-duty law enforcement officers from carrying weapons on its campus. She declined to discuss further Silverman's possession of a weapon.
"As this is an ongoing investigation, we remain focused on working with the Delaware County Police Departments to understand fully the details of the event and to do all we can to assist those affected," said the spokeswoman, Bernice Ho.
Yeadon Police Chief Donald Molineux said that "without a doubt, I believe the doctor saved lives."
"Without that firearm, this guy (the patient) could have went out in the hallway and just walked down the offices until he ran out of ammunition," the chief said.
Plotts does not have a listed home phone number. Court records in Delaware County show a man of the same name and age with a lengthy criminal record, but Whelan was unsure if it was the same person.
Two guns were recovered from the scene, Whelan said.
Staff members had heard loud arguing inside Silverman's office during the appointment. They opened the door and noticed the patient had a gun pointed at the doctor, so they quietly closed the door and dialed 911, Whelan said. Gunshots were heard a short time later, just before 2:30 p.m.
Plotts, severely wounded from several shots, emerged from the office, and another doctor and a caseworker helped wrestle him to the floor of the hallway and grabbed his weapon, Whelan said.
"They acted vigilantly. They acted bravely," he said.
The exchange of gunfire occurred on the third floor of the Wellness Center at Mercy Fitzgerald, a 204-bed community teaching hospital. Authorities said there are no surveillance cameras in the doctor's office or the waiting area outside. They also said the center had no metal detectors.
Patients waiting in the first-floor lobby reported a tense scene when police arrived and ordered everyone out. Most of the patients were elderly.
"I dozed off, and I heard the cop shouting, 'Come on, come on, get out!'" said Millicent Russell, of Lansdowne, who was waiting for a 3 p.m. appointment. "There were people with walkers and canes and stuff. All these cops were outside running here and there with these guns."
Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.