DARBY, Pa. (AP) — A doctor who was grazed by gunfire from a patient in his office at a suburban hospital on Thursday helped stop him by apparently returning fire with his own weapon and severely injuring him, but not before a caseworker was killed, authorities said.

The patient opened fire after entering the office with the caseworker, District Attorney Jack Whelan said. Witnesses reported hearing yelling before the gunshots.

Several hours after the shooting, investigators had only limited information on what happened inside the closed office but believe the doctor, a psychiatrist, “from all accounts, would have acted in self-defense,” Whelan said.

The doctor, who suffered a graze wound to his head, “faced a situation where his life was in jeopardy,” Whelan said.

The dead caseworker was identified only as a 53-year-old woman who had entered the doctor’s office with the patient before the gunfire erupted.

Two guns were recovered, Whelan said. Authorities said the motive for the shooting was unknown. 

The patient, who was in custody, was described as a man in his 30s from nearby Upper Darby.

Another doctor and a caseworker were among those who helped wrestle the patient to the floor of a hallway and grabbed his weapon after he had already been critically wounded from several gunshots, Whelan said.

“They acted vigilantly. They acted bravely,” Whalen said. 

The exchange of gunfire occurred on the third floor of the Wellness Center at Mercy Fitzgerald Hospital, a 204-bed community teaching hospital just southwest of Philadelphia.

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.

“Do you evaluate that now ... in light of this incident to make sure people are safe, especially in what can be a dangerous environment?” Whelan asked.

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, 73, 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.”