(Reuters) - Police in three states searched on Saturday for a gunman who ambushed two state troopers, killing one of them, in an attack at a law enforcement barracks in Pennsylvania, police said.

Police said they were questioning a man about the shooting, which occurred about 100 miles (161 km) north of Philadelphia at the Blooming Grove barracks around 11 p.m. local time on Friday (0300 GMT Saturday), but they stressed that the search was still under way for anyone involved in the attack.

“It seems to be an attack on law enforcement and our form of government,” Pennsylvania State Police Commissioner Frank Noonan said during a news conference.

With the shooter still on the loose on Saturday, law enforcement officers fanned out across Pennsylvania, New York and New Jersey in a manhunt, Noonan said.

“I know a lot of people are wondering if the threat is resolved. It is not,” he said. “The individual who perpetrated this heinous crime is still at large.”

Noonan, who added that more than one suspect might have been involved, said police do not have a description or any information on who committed the attack.

On Saturday morning, police interviewed a man described as a person of interest, said Connie Devens, a state police spokeswoman. She said he was not under arrest and no further details were immediately available.

Noonan said that anyone interviewed at this stage of the investigation was not necessarily a suspect.

He said the troopers were ambushed but would not share details of the incident because it was still under investigation.

Noonan identified the slain trooper as Corporal Bryon Dickson.

Trooper Alex Douglass, who was wounded in the ambush, underwent surgery at a hospital and was in critical but stable condition, Noonan said.

Blooming Grove is a township of roughly 5,000 people near the New York state border.

Pennsylvania Governor Tom Corbett in a statement called on the public to be vigilant as law enforcement officers conduct a search for anyone who was involved in the attack.

“Every attack on an officer of the law is an attack on our state, our country and civilized society,” he said.