Authorities searching for accused cop killer Eric Frein in Pennsylvania got a big break when the suspect slipped-up and used his cellphone to contact his parents.

The Philadelphia Inquirer reported the Sept. 18 call lasted only seconds, but that was long enough for investigators to draw a bead on his whereabouts.

As a result of that call the manhunt for Frein was narrowed to a five-square mile perimeter in Monroe and Pike counties, the paper said Friday citing sources with knowledge of the investigation.

The Inquirer said it was unclear why Frein turned on his phone. It said investigators have spotted him more than once since the call but are proceeding with extreme caution because they believe Frein may have booby-trapped the area where he is hiding with pipe bombs.

Frien, 31, allegedly killed Pennsylvania State Trooper Bryan Dickson and injured a second trooper in an ambush outside the state police barracks in Blooming Grove two weeks ago.

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State Police Lt. Col. George Bivens said a police inspection of the hard drive shows Eric Frein did Internet research on how to avoid police manhunts and on law enforcement technology and survival skills.

Bivens said Frein might now be treating the dragnet in northeastern Pennsylvania as "a game — a war game, if you will."

Frein has managed to elude hundreds of law enforcement officials looking for him in the thick woods around his parents' home in Canadensis, taking advantage of the difficult terrain to keep them at bay. He is believed to be armed with at least one high-powered rifle.

"I suspect he wants to have a fight with the state police, but I think that involves hiding and running since that seems to be the way he operates," Bivens said. "I expect that he'll be hiding and try to take a shot from some distance from a place of concealment, as he has done in the past."

Underscoring the danger they face as they pursue him, Bivens said Frein had experimented with explosives, citing materials that police found and interviews with people who knew him. Trackers are proceeding through the thick woods as though they are booby-trapped, he said. Police think Frein might have a radio.

A police dog picked up Frein's scent several days ago and flushed him from his hiding place. But the distance was too great, and Frein was able to get away, the dense canopy providing cover from a police helicopter overhead, Bivens said Friday.

As the search for the gunman neared its third week, Bivens said he remains confident police will catch their man — "at some point."

The Associated Press contributed to this report