MEDIA, Pa. — A psychiatric patient who killed his caseworker — and grazed his psychiatrist before the doctor pulled out his own weapon and fired back — has a lengthy history of gun arrests, violence and mental health problems, authorities said.

Dr. Lee Silverman emptied his gun’s chamber, striking patient Richard Plotts several times, Delaware County District Attorney Jack Whelan said. Plotts by then had shot the caseworker in the face and fired several shots at Silverman, including one that grazed his temple and another that struck his thumb, he said.

Plotts had 39 unspent bullets on him when he was wrestled to the ground at Mercy Fitzgerald Hospital in Darby, just southwest of Philadelphia, and police believe he had planned to use them.

“If the doctor did not have a firearm, (and) the doctor did not utilize the firearm, he’d be dead today, and I believe that other people in that facility would also be dead,” Whelan said.

Police in Upper Darby, where Plotts lived, were aware of at least three mental health commitments — including once after he cut his wrists and once when he threatened suicide — but said such stays can last just one to three days.