Police identified the motorist as James D. Toliver, 32, of Upper Marlboro. He was taken to a hospital and died several hours later, police said.
Officials identified the officer as Cpl. Michael Mogavero, a nine-year veteran who is assigned to the special operations division. He was treated for minor injuries at a hospital and released.
Police said they had started a thorough investigation but were prepared to release few details.
“It is a tragic event,” Deputy Chief Hector Velez, the department’s head of patrol, said at a news conference. “We want to let everybody know what occurred and know that we are investigating the incident, and we will provide updates as they come along.”
Velez said police are operating on the assumption that the officer was driving with his lights and siren on, which should have activated the cruiser’s dashboard camera. He said investigators were working Wednesday to retrieve the video.
Lt. William Alexander, a police spokesman, said it was unclear how fast the officer was traveling and whether the traffic signal at the intersection was functioning with green and red lights or if it had shifted to yellow flashing lights, as many in the area do late at night.
Police said they also were working to determine whether Toliver was trying to cross the intersection or turn right onto Route 197.
“We don’t know who had the green, yellow, red, or what. The issue of right of way is all part of the ongoing investigation,” Alexander said.
But there was no dispute that the crash came with horrible irony.
Mogavero, a member of a special traffic enforcement unit, was on his way to investigate an accident involving another county police officer in Oxon Hill.
The details of that first crash were not immediately released Wednesday. Until six months ago, Prince George’s officers would not have traversed the county to investigate minor accidents involving colleagues.
But after two accidents in which Prince George’s officers were killed last year, the department instituted reforms designed to make investigations more objective. Under one of those new rules, an officer’s direct supervisor can no longer write a report when his subordinate is involved in an accident. That must be done by a member of a special unit that investigates all officer-involved accidents.
Wednesday’s accident is being investigated by yet another division within the department with authority over all fatal accidents. At the end of the investigation, Velez said, the department’s top chiefs and inspector general would meet with the county’s state’s attorney to review the evidence.