Investigators on Sunday returned to scour the woods across from a state police barracks where two troopers were ambushed, leaving one fatally shot and another critically wounded.

The probe comes as a nonprofit group offered a $50,000 reward for tips about Friday's deadly assault at the remote post in northeast Pennsylvania.

Eight investigators walked into the dense forest in Blooming Grove around noon Sunday, The Times-Tribune reported. A day earlier, authorities suggested the suspect had left the area.

Police had released no new information about the case as of mid-afternoon.

The troopers were ambushed around 10:50 p.m. Friday as one of them was leaving the barracks and another was arriving. Cpl. Bryon Dickson of Dunmore was killed and Trooper Alex Douglass was injured.

Dickson, a seven-year veteran, had transferred to the region from the Philadelphia barracks several months ago. Taken to a hospital, Douglass underwent surgery and was in critical but stable condition.

Pennsylvania State Police Commissioner Frank Noonan said the "cowardly attack" was directed at state police and a "very dangerous, armed criminal" eluded quick capture.

"Our troopers were ... shot without warning and really had no chance to defend themselves," Noonan told reporters Saturday afternoon. "It has touched us to the core that such a thing could happen."

Pennsylvania Crime Stoppers, which posted the reward offer, asked anyone with information to call 800-4PA-TIPS or submit the tip online.

Law enforcement officers from at least three states on Saturday searched state game lands surrounding the barracks in Pike County and beyond.

"There has been an exhaustive search conducted by hundreds of members of law enforcement," said Lt. Colonel George Bivens. "We have canvassed the wooded areas, neighborhoods. We are convinced this individual is no longer in that immediate area."

Police interviewed a man they called a "person of interest," but Noonan said authorities are talking to hundreds of people as part of the investigation. He stressed the man is not a suspect.

The slain trooper was married with two young sons. He was described by friends as devoted to work and family.

"They were a committed couple," Melissa Contorno, a friend of Dickson's wife, told The Times-Tribune. "They were raising a beautiful young family. It's not fair."

Blooming Grove is a township of about 4,000 people about 35 miles east of Scranton. State police spokesman Trooper Adam Reed said the barracks cover most of Pike County, a primarily rural area that runs along the Delaware River and borders New Jersey and New York.