Lakewood, Washington (CNN) -- A shooter who killed four police officers Sunday in a coffee shop outside Tacoma, Washington, may have sustained a gunshot wound from one of the victims before he fled on foot, police said.
Investigators are checking with area hospitals to determine whether the gunman sought medical treatment after the shooting, Pierce County sheriff's spokesman Ed Troyer said.
Four Lakewood officers were sitting in the coffee shop in neighboring Parkland before the start of their shifts, reading their computers, when the shooting happened, Troyer said. Authorities believe the officers were meeting and going over cases or doing paperwork, he said.
"This was a targeted, selected ambush," Troyer said.
Troyer said a gunman came inside and shot all four officers at about 8 a.m. PT. Two coffee shop employees and other customers inside the shop were unharmed, he said.
"As you can imagine, they are traumatized," he said of those inside the coffee shop. "Some are in shock."
Police are looking for one man in connection with the attack, though authorities are not ruling out the possibility that a second person was involved, Troyer said. A $10,000 reward was offered for information leading to an arrest, he said.
Families of the officers have been notified, Troyer said. All of the officers -- three males and a female -- were in uniform, wearing vests and had marked patrol cars parked outside, he said.
Health Top Tips Nutrition Love Lifestyle Happiness Weight LossAuthorities were conducting searches in numerous locations, and dogs had been brought in to attempt to track the suspect, Troyer said. Some tips have come in, and investigators were following leads, he said.
A couple of blocks surrounding the coffee shop were cordoned off. Several other police agencies were on scene to assist.
There were no known threats against police before the incident, Troyer said.
Washington Gov. Christine Gregoire, in a statement, said she was "shocked and horrified" at the shootings.
"I offer whatever support is needed to the Pierce County Sheriff in their search for the perpetrator," Gregoire said.
Lakewood is about 40 miles south of Seattle and 10 miles southwest of Tacoma.
See a map of where the shootings took place
Bystanders gathered outside the Forza Coffee Company, some of them in tears as they spoke to CNN affiliate KING.
The coffee shop is on the edge of McChord Air Force Base. Spokesman Bud McKay said the base was not shut down, but security was ramped up around the perimeter as a precaution.
The military has offered assistance to police, he said, but it has not been requested.