State police searching for a man accused of killing a trooper and wounding another said Tuesday they found two pipe bombs capable of causing "significant damage" in the Pennsylvania woods during their search.

The bombs were not deployed, but they were fully functional and could have been set off by either a trip wire or a fuse, Lt. Col. George Bivens said.

They were among several items that were "clearly hastily discarded" at a campsite used by suspect Eric Frein, Bivens said at a news conference. He then called on Frein to surrender.

"You are clearly stressed," Bivens said. "You are making significant mistakes."

Frein, 31, has been on the run since Sept. 12, charged with killing one state trooper and wounding a second outside their barracks in Blooming Grove.

Authorities believe the self-taught survivalist is hiding in the rugged terrain near his parents' home in the Pocono Mountains. But Bivens said Tuesday that he doesn't believe this was Frein's original getaway plan.

Frein's car was found submerged in a swamp several from the barracks a few days after the shooting.

"I think things went wrong with his plan," Bivens said.

Bivens said there has been at least one credible sighting of Frein in the past 24 hours, from between 75 yards and 100 yards away through thick woods.

Police said last week they were treating the search area as if it was booby-trapped, because of evidence Frein had been experimenting with explosives.

The pipe bombs had the capability of causing substantial damage, Bivens said.

Law enforcement officers have also found several structures where they believe Frein has stayed.

The Associated Press contributed to this report.