It's been nine days since alleged gunman Eric Frein opened fire at a Pennsylvania police barracks, killing one officer and injuring another, and police have yet to discover his whereabouts. On Sunday, police conducting the search announced they'd discovered a rifle Frein had abandoned in the woods.

The Associated Press reports that Pennsylvania State Police Lt. Col. George Bivens believes that Frein, a "self-taught survivalist," had been planning an altercation with police for months, potentially years.

Via the AP:

Bivens said Frein had the advantage of knowing the "rugged terrain" around the area initially, but does not any longer.

"Our tactical operations people now also know his backyard, the area he once felt safe in," Bivens said.

No contact had been made with Frein, who was placed on the FBI's Most Wanted list after the Sept. 12 shooting at a nearby police barracks that left one trooper dead and a second wounded.

Police are scouring Pike and Monroe counties, near where the alleged shooter grew up. Residents are being asked to exhibit caution, locking doors and windows, and to report any suspicious people or activities. The police do not believe that Frein is being helped at all and has likely covered over 15-20 miles since the shooting last week.

[Image via AP]