Police in Newport Beach, California are investigating the murder of an Orange County doctor in his exam room by one of his own patients.

Dr. Ronald Gilbert, a urologist, was found shot to death in a patient exam room on Monday afternoon. Police say callers reported hearing seven or eight shots at about 2:45 p.m. Gilbert was declared dead at the scene.

When police arrived about eight minutes after the first calls, they took a 75-year-old man into custody in the room where the shooting happened. Police confirmed to ABC News the man was a patient of Dr. Gilbert, but said they are still investigating a possible motive.

The suspect, identified as Stanwood Fred Elkus by ABC station KABC-TV, has remained cooperative during the investigation.

Newport Beach Police spokesperson Kathy Lowe said officers searched Elkus' home and found evidence that might point to a possible motive, KABC reported, although circumstances of the shooting remain unclear.

"It's going to be part of our ongoing investigation to determine the exact motive for this crime," Lowe said.

Medical staff at the Hoag Health Center, where the shooting occurred, were put on lockdown after the shooting, but the building reopened today.

Hoag's president and CEO, Richard Afable, said in a statement that Dr. Gilbert had been on staff there for nearly 20 years.

"He was admired, respected and beloved by the Hoag family and will be deeply missed," the statement read.

Elkus is being held on $1 million bail, and is scheduled to be arraigned Wednesday, KABC reported.