BLOOMING GROVE, Pa. -- There was a killer on the loose Wednesday night, and the police say he is Eric Frein, who is charged with ambushing two Pennsylvania state troopers last Friday night, shooting them with a rifle.

One was killed. The other remains in critical condition.

The police describe Frein as a self-trained survivalist with a grudge against law enforcement who has talked about committing mass murder.

Hundreds of officers are looking for him in a heavily wooded area of Pennsylvania. Searchers have to make their way through rugged terrain with thick underbrush and hills.

The man they're looking for is said to be very familiar with these woods. He is heavily armed and extremely dangerous.

Wearing full camouflage and body armor, grim-faced officers geared up for a sixth day of searching the dense forest.

They're hunting a man who might also be hunting them.

"I want you to know one thing: Eric, we are coming for you," said Lt. Col. George Bivens of the Pennsylvania State Police.

The 31-year-old Frein is suspected of lying in wait just before midnight Friday in front of the state police barracks in Blooming Grove just as a shift changed.

Pennsylvania State Police Cpl. Bryon Dickson

He allegedly shot and killed Cpl. Bryon Dickson and seriously wounded Trooper Alex Douglass.

Pennsylvania State Police Trooper Alex Douglass

"It's a cowardly act," said Pike County Sheriff Philip Bueki. "The troopers did not have a chance. They didn't even know what had hit them."

Two days after the shootings, Frein's car was discovered partially submerged in a pond two miles from the barracks. Officers say they found evidence in it linking him to the ambush, including shell casings and his driver's license.

The son of a retired Army major, Frein was a member of a group who dressed up in Eastern European military garb and played war games. In 2007, Frein also played a German soldier in a short independent film. His father described him as an expert marksman who can't miss.

More than a dozen schools in the area were shut down Wednesday. Lisa Leonawicz only ventured out to get food.

"If he does that to police officers, then he can do anything to anybody," she said.

Police say Frein has shaved the side of his head and has grown the top hair long in sort of a bushy Mohawk. He is believed to be armed with an AK-47 as well as a .308-caliber hunting rifle with a scope.