The possibility that Eric Frein might be lurking nearby was never far from Trooper Ryan Lawrence's mind as he took part in the manhunt for the 31-year-old survivalist charged with ambushing a Pennsylvania State Police barracks three weeks ago.

Lawrence recently spent five days in the search zone, working a 12-hour overnight shift on road and perimeter patrol.

"You definitely have to stay within a tactical mindset, just so you're not opening yourself up for a possible attack, at least limiting the possibility of making yourself a target," Lawrence said Friday.

The trooper would keep himself out of the glare cast by his car's headlights, for instance, giving him the ability to observe but not easily be observed.

Hundreds of law enforcement officials have been searching for Frein, of Canadensis, who's charged with killing Cpl. Bryon Dickson and seriously wounding Trooper Alex Douglass in the late-night attack outside the Blooming Grove barracks.

The manhunt is concentrated on a heavily forested area around the northeastern Pennsylvania home where Frein lived with his parents.

State police Lt. Col. George Bivens planned to hold a news conference Friday afternoon to provide an update on the search, which has drawn law enforcement officials from New York and New Jersey state police, the FBI, the U.S. Marshals Service and other federal agencies.

Frein has been described as an anti-law enforcement survivalist and expert marksman at home in the woods. He's considered armed and dangerous.

Even as the manhunt wrapped up its third full week, police said they remain confident Frein will be caught.

"It's just a matter of time for him," Lawrence said. "The commissioner down to every road trooper has the same resolve."

Lawrence lives in Lancaster, about 100 miles from the search area. Troopers throughout Pennsylvania are signing up to search for Frein, he said.

"The driving force is obviously for the family of Cpl. Bryon Dickson. It's a commonly spoken thing while there, you are doing it for him and his family," Lawrence said. "There's a wife and two sons who aren't able to have their state trooper come home, and that's a driving force for a lot of our guys up there."