Authorities say accused cop-killer Eric Frein used a computer to research how to avoid police manhunts and use law enforcement technologies and skills related to survival.

That leads authorities to believe that he planned his Sept. 12 ambush attack on two state troopers at the Blooming Grove barracks in Pike County for at least two years."I believe he has plotted for an extended period of time to make an attack on someone and that he has studied survival skills and evading law enforcement for that extended period of time," Pennsylvania State Police Lt. Col George Bivens said at a news conference Friday.But Frein removed the hard drive from his own computer before shooting Cpl. Bryon Dickson and Trooper Alex Douglass, Bivens said.Dickson, 38, was killed; Douglass remains in critical condition.The computer hard drive on which the evidence was found was not Frein's, but was not a public computer, Bivens said. He said police also found searches that Frein had tried to hide or delete. Bivens did not specify what those searches were for.For two weeks, law enforcement authorities at the state and federal levels have continued to comb the rugged forests, with thick canopies and innumerable caves and outcroppings, near the border of Monroe and Pike counties. The search has been focused on Barrett and Price townships, near Frein's Canadensis home.Last sighting"The search area is very large, and the terrain is dense and rugged," Bivens said.He said tracking dogs at one point several days ago caused Frein to "jump out at quite some distance ahead of us." owever, he said that darkness was falling, the foliage thick, and Frein was very far away, so there was no chance of capture.The last sighting of Frein was about three days ago. Police believe Frein may be carrying a radio."There is nothing in our investigation that indicates Frein has left the area," Bivens said. "I believe we're close. I believe he's in the area. I believe we'll find him."Police learned from materials they found and from interviews that Frein apparently "experimented" with explosives, Bivens said. Police are aware of the possibility that he may have planted booby traps in the woods.Bivens again warned people to stay out of the woods in Barrett and Price townships and Delaware State Forest."He is absolutely still a threat to not only the police but to the public," he said.Bivens said police are authorized to use lethal force if Frein is positively identified and refuses to surrender."I suspect that he wants a fight with state police, but I think that involved hiding and running, since that seems to be the way he operates. He's probably not going to come out and have a face-to-face confrontation. I expect he'll be hiding and trying to take a shot from some distance from a place of concealment, as he's done in the past."In their exhaustive search, police have found evidence of tampering with some abandoned or vacant sheds, garages and homes, but have yet to determine whether items found in them belong to Frein.Frein was well-prepared and probably hid things out in the woods or in structures, Bivens said. Police have also investigated purchases Frein made before the shooting, perhaps to build a bunker.Addressing rumorsBivens also addressed "troubling rumors" concerning Frein's sister-in-law, Melissa Frein, having an affair with Douglass, who also lives in the area.Bivens said that's not true, that Douglass did not even know Melissa Frein or her husband, Michael."Through many investigative techniques, state police have found no evidence of an inappropriate relationship between trooper Douglass and Melissa Frein. We cannot assume to know what Eric frein believes. However, we are convinced Trooper Douglass and Melissa Frein did not have a personal relationship."Bivens said police did search Michael Frein's home to rule out co-conspirators early in the investigation. They believe Frein acted alone.On Friday, police searched the abandoned, massive Buck Hill Inn in Barrett Township. Bivens said Frein is believed to have visited the old stone structure after it closed.Frein, 31, is believed to have ambushed the troopers during a shift change at 10:50 p.m. Sept. 12. Police believe Frein was hiding in the woods across from the barracks when he shot at the troopers.A man walking his dog about two miles from the barracks on Sept. 15 found Frein's Jeep partially sunk in a retention pond. Police found evidence in the Jeep, including Frein's Social Security card, driver's license and other items that led to his identification, as well as spent shell casings that matched bullets found at the barracks. A subsequent search of Frein's home revealed more ammunition of the same type.Frein, an expert marksman, self-styled survivalist and war game aficionado, is believed to be armed, and hiding out in the rugged forests surrounding his home. Police have used thermal imaging, dogs and other methods as they comb the area. They have discovered an AK47 he had hidden, as well as adult diapers and a pack of the Serbian cigarettes Frein favors.As he has before, Bivens on Friday addressed Frein directly."Eric, as I told you last week, you are a coward. Your actions have caused tremendous disruption for an innocent community, all while you try to hide from us. We are not intimidated. We will not leave. We have a clear mission with specific objectives. We will protect the community. We will find you. And we will bring you to justice."