Police have identified a suspect in the shooting of a Pennsylvania state trooper and warned that they have been unable to locate the gunman, who they say has expressed a desire to “commit mass acts of murder.”

Frank Noonan, commissioner of the Pennsylvania State Police, said Tuesday that arrest warrants had been issued for Eric Matthew Frein, 31, of Canadensis, Pa. A manhunt is underway to find Frein, who is “armed and extremely dangerous,” Noonan said during a news conference.

Frein has been charged with murder, assault and several other counts following the shooting Friday night near a state police barracks in Blooming Grove, in the northeastern corner of the state.

Cpl. Bryon Dickson was killed, while another trooper, Alex Douglass, was seriously wounded. Noonan later described the shooting as “an ambush,” saying that the troopers were shot without warning while one was heading to the barracks and the other was leaving it.

The office of Pennsylvania Attorney General Kathleen G. Kane released this photo of Frein and called on anyone with any information to call the state police tip line:

Shell casings matching those used in the shooting were discovered in a vehicle not far from the barracks, along with information that identified Frein, Noonan said.

Noonan described Frein as a “survivalist” and said he has spoken before about killing police officers and other people.

“He has made statements about wanting to kill law enforcement officers and also to commit mass acts of murder,” Noonan said. “What his reasons are, we don’t know. But he has very strong feelings about law enforcement and seems to be very angry with a lot of things that go on in our society.”

Authorities have warned in recent years that people with particularly violent feelings toward law enforcement officers could pose a growing threat and target such officers or government officials. The number of ambushes of police officers has also increased in recent years, according to the National Law Enforcement Partnership to Prevent Gun Violence.

A large search effort involving about 200 officers is searching a forest-covered stretch of Pennsylvania for Frein, according to police. But they had not been able to locate him as of Tuesday afternoon.

“Every attack on an officer of the law is an attack on our state, our country and civilized society,” Pennsylvania Gov. Tom Corbett said in a statement after the shooting. “The incident in Blooming Grove shows, once again, that our first responders face constant danger in order that the rest of us may live in peace and safety.”