Michael J. Mullen, Associated Press
Pennsylvania Gov.Tom Corbett second right, speaks to the press at the Blooming Grove Baptist Church in Pike County, Pa., Monday, Sept. 15, 2014, about the shooting Friday night that took the life of a Pennsylvania State Police trooper and critically injured another. Corbett said investigators won't rest until they capture the gunman.

The killer had a grudge against the Pennsylvania State Police. He regularly visited a local shooting range to keep his skills sharp. He made several trips to a state police barracks in northeastern Pennsylvania, picking just the right hiding spot from which he could launch an ambush and make his escape.

This chilling profile, developed by state police hunting for the gunman who opened fire on two of their own outside the Blooming Grove barracks late Friday, was released to the public Monday in hopes it might help authorities catch him.

An unknown assailant, using a .308-caliber rifle, killed Cpl. Bryon Dickson, 38, and critically wounded another trooper at the remote outpost surrounded by dense forest, then slipped away. The motive is unknown, but police said Monday it's likely he had a grievance against the state police and wasn't shy about talking about it, either with people who knew him or on social media.

Authorities believe he may be an avid hunter or received firearms training, possibly from law enforcement or even the military.

Addressing the "coward" who "did it from a place of hiding and ran," Lt. Col. George Bivens vowed Monday that police will make an arrest.

"I want you to know that troopers are working around the clock to bring you to justice," Bivens said. "The act that you committed may have been meant as an act of intimidation. It has not intimidated us. The Pennsylvania State Police is committed to bringing you to justice. We will find you and we will seek justice when we do."

Police received hundreds of tips as a nonprofit group increased its reward offer to $75,000 for information leading to the gunman's capture, and a number of the tips provided "credible information" about the ambush, Bivens said. Pennsylvania Crime Stoppers has asked anyone with information to call them or submit tips online.

Several law enforcement agencies, including the FBI, were helping with the investigation. Authorities pored over old cases investigated by the two troopers — and by others in the barracks and elsewhere — in hopes of turning up a suspect.

Trooper Tom Kelly said in a statement early Tuesday that parts of Route 402 were blocked in some areas overnight to allow a search of the area without endangering the safety of motorists. He didn't say what investigators were looking for, but said the road has been reopened and no one is in custody.

As the manhunt continued, Dickson's family prepared for his funeral, to be held Thursday at a Roman Catholic cathedral in Scranton. Dickson, a Marine Corps veteran who joined the state police in 2007 and had worked as a patrol unit supervisor in the Blooming Grove barracks since June, is survived by his wife of 10 years and two young sons.

Douglass, a nine-year veteran, was conscious and talking for the first time since he underwent surgery. Investigators planned to interview him.

Earlier Monday, Gov. Tom Corbett said investigators won't rest until they capture the gunman, and asked the public to "pray for the soul" of Dickson. The governor, who toured the crime scene, called Dickson's killing an assassination and planned to meet with family members.

"This is an assault that was not only just on the individual troopers, it's an assault on the state police, it's an assault on law enforcement, it's an assault on society," Corbett said.