An 18-year-old gunman opened fire outside a suburban Washington police station Monday, killing one officer and wounding two others before he was shot and killed, authorities said. No motive was disclosed.

A 40-year-old female detective died at a hospital after the shooting, said police Chief David Rohrer, who did not identify the woman, a nine-year veteran of the Fairfax County Police Department.

A second officer was in serious condition and undergoing surgery late Monday. A third was treated for minor injuries from flying glass or a ricocheting bullet.

Authorities did not divulge the gunman's name. They were uncertain whether he shot himself or was killed in the exchange of gunfire.

"It's going to be unraveling slowly," police spokeswoman Mary Ann Jennings said. "We don't have a clue at this point. I'm sure some of the investigators are starting to put that together."

Jennings said the gunman had a rifle and two handguns and had stolen a van that he drove to the station after unsuccessfully attempting to carjack a pickup truck. It was unknown "exactly who he was targeting except to say he was targeting police officers," she said.

Fairfax County police officer Rich Henry said the gunman opened fire during mid-afternoon in a back parking lot at the Sully District Station.

For hours after the shootings, roads were blocked and nearby buildings, including a high school, were locked down as police sought other possible suspects. Investigators later determined there was just one gunman, said police spokeswoman Lt. Amy Lubas.