Eric Frein's Handwritten Note Found During Manhunt: Police

— -- A handwritten letter penned by Eric Frein has been found in the Pennsylvania woods as police continue to scour the area looking for the accused cop shooter, authorities said today.

Details in the letter lead police to believe it was written by Frein, who's been on the run since Sept. 12.

The note offers no motive for the shooting death of Cpl. Bryon Dickson and the wounding of another trooper when Frein allegedly ambushed the Blooming Grove police barracks, a law enforcement official familiar with the case told ABC News.

It's not clear whether the letter, first reported by CNN, was left intentionally or by accident.

The note is the latest clue in a massive manhunt -- with police focusing on an area near the border of Pike and Monroe counties in eastern Pennsylvania, the place they believe Frein, 31, has been hiding.

Police said on Friday they found a campsite where Frein had stashed food, ammunition, clothing and other supplies. Police have also found an AK-47, two "fully functional" pipe bombs, soiled diapers and Serbian cigarettes in the manhunt.

Frein, from nearby Canadensis, has been spotted several times, but always evaded police capture because of the thick terrain.

Lt. Col. George Bivens has said the suspect may consider the chase "a game" and has repeatedly called for him to surrender.

Police said they hope the colder weather will eventually force the suspect out of the woods.

Frein is a self-trained survivalist and war reenactor who focused on Eastern European militaries and weapons. He learned to shoot from his father, a retired Army major.

Bivens has said Frein's family has been cooperative.

People who knew Frein have described him as "goofy but dark," and one former colleague even suggested that he was imitating the movie character Rambo when he allegedly opened fire on the troopers.

The FBI is also involved in the manhunt and has added Frein to its 10 Most Wanted Fugitive List.

Get real-time updates as this story unfolds. To start, just "star" this story in ABC News' phone app. Download ABC News for iPhone here or ABC News for Android here. To be notified about our live weekend digital reports, tap here.