The Furious, Close-Range Gun Battle in Pa. Hospital
PHOTO: A hospital worker views police activity near the scene of a shooting at a wellness center attached to Mercy Fitzgerald Hospital in Darby, Pa., July 24, 2014.

A doctor with a semi-automatic gun and a caseworker who was "nothing short of heroic" were able to wound and then subdue an armed psychiatric patient after he had killed another caseworker and appeared intent of reloading and shooting more people in a Pennsylvania hospital, police said today.

The patient, Richard Plotts, 49, suddenly pulled a gun out of his waistband and shot his caseworker, Theresa Hunt, in the head at point blank range while inside psychiatrist Lee Silverman's office for a scheduled appointment on Thursday. Hunt was killed instantly, authorities said.

Silverman dove to the floor, pulled a semi-automatic pistol out his pocket and had a furious close range gun battle with Plotts, who police said fired at least 10 rounds. The doctor, who was using a chair for protection, aimed his gun at Plotts and fired until it was empty, District Attorney Jack Whelan said today in recounting what happened.

Cause Sought for Gunfight Between Patient, Doctor

The doctor, who was grazed in the head and wounded in the thumb while covering his face, was able to get out of the office, unaware that he had struck Plotts three times.

According to Whelan, caseworker John D'Alonzo heard the shooting and called 911. He then climbed through a window into Silverman's office because the door was locked and "engaged in a wrestling match with Mr. Plotts," getting him on the ground. Whelan called D'Alonzo's actions "nothing short of heroic." Dr. Jeffrey Dekret helped D'Alonzo wrestle the gun away from Plotts and hold him for police, Whelan said.

Whelan said that D'Alonzo "believed Plotts was trying to reload." The prosecutor said Plotts had another 39 bullets.

"If it wasn’t for the heroic actions" of Silverman and Dalonzo, "we believe he (Plotts) was going to reload that revolver and continue to fire," Whelan said.

Plotts has been charged with murder, attempted murder and weapon charges in Thursday's shooting. Whelan said Plotts was in stable but guarded condition and was sedated. His arraignment would be held when Plotts was no longer sedated, the DA said.

Plotts, who Silverman has known for 20 years, arrived early for an appointment with a gun hidden in his waistband.

"He intended to kill Dr. Silverman and that’s why he brought the gun," Whelan said. The motive for the shooting was not yet known, he said.

Silverman has a license to carry a concealed weapon, Whelan said, and state policy says that it is legal to have a concealed weapon in a home or office, though it is unclear whether or not the hospital's policy permits employees to be armed.

"I believe it was his practice for his own self protection to carry a firearm," Whelan said. The prosecutor said that had the doctor not had a gun and fired back, "he would probably not be alive today," Whelan said.

Plotts had a history of violence with arrests for simple assault and a federal bank robbery as well as illegal firearms possession.

Plotts did not have a license for the gun that he used.

More ABC News