Notes found in the woods by alleged cop killer Eric Frein offered a "cold-blooded" and "chilling" account of how he shot and killed a Pennsylvania State trooper last month before escaping into the vast forest in the Pocono mountain region, authorities said.

Law enforcement officials scouring the dense, rugged terrain for Frein found signs the 31-year-old survivalist has hid in rock caves and lit small fires to evade capture, Lt. Col. George Bivens, deputy commissioner of operations, said at a news conference in Blooming Grove Wednesday afternoon. Authorities also said there have been four reported sightings of Frein in the area since Friday – some by local residents.

Frein is charged with opening fire outside the rural Blooming Grove state police barracks on Sept. 12., killing Cpl. Bryon Dickson and seriously injuring Trooper Alex Douglass in the attack. Additional charges have also been filed following the discovery of explosives allegedly set by Frein that Bivens labeled "weapons of mass destruction."

On "multiple pieces of paper" found in the woods by investigators, Frein allegedly described the deadly ambush and how he managed to escape into the woods around his parents' home in Canadensis.

"Got a shot around 11 p.m. and took it," Bivens quoted Frein as writing. "He [Dickson] dropped. I was surprised at how quick."

Bivens, who read excerpts of the notes to reporters, says Frein wrote he tried to make his getaway in a Jeep, but ran it into a swamp and took off on foot. He says Frein called the botched getaway a "disaster."

"I can only describe his actions as pure evil," Bivens said

"He is someone who has clearly practiced the art of hiding," he said. "The Pennsylvania State Police didn’t pick this fight but it is ours to finish ... We're not going anywhere. We will get Frein."

Bivens said force will be used if Frein fails to "actively surrender."

FoxNews.com's Cristina Corbin contributed to this report.