Investigators found two fully functional pipe bombs and believe that a three-week manhunt may be taking a toll on suspected cop killer Eric Matthew Frein , Pennsylvania State Police Lt. Col. George Bivens said Tuesday . `` Over the last few days we have found several items that undoubtedly confirm Eric Frein is hiding in our search area , '' Bivens told reporters . `` We have found a number of items belonging to Frein , some of which were hastily discarded . '' Those items include a pair of pipe bombs found in the last two days that could be detonated via trip wire or fuse -- consistent with what Bivens called `` Frein 's non-confrontational and gutless efforts to kill or injure law enforcement from a distance . '' The bombs were capable of causing significant damage , he said . `` I ca n't get into his head but I 'm sure that he is stressed at this point , '' Bivens said . `` It 's been a couple of weeks and I am certain that he is not sleeping well at night . '' Frein may have been spotted within the past 24 hours in the rugged area where he has been sighted numerous times , Bivens told reporters . The suspect was wearing dark clothing and was seen between 75 and 100 yards away . `` We 're confident that he 's in the area , '' Bivens said . Frein is sought in the death of Cpl . Bryon Dickson in a September 12 ambush outside the state police barracks in Blooming Grove . Trooper Alex T. Douglass was wounded in the attack . Authorities have located several structures where they believe the suspect has stayed . Some items were found in a location that Frein may have used as an `` overnight accommodation , '' Bivens said . 'We are not going anywhere ' As he has in the past , Bivens , who is spearheading the manhunt , had a personal message for Frein : `` I am calling on you , Eric , to surrender . You are clearly stressed . You are making significant mistakes . We continue to take your supplies and your weapon stockpiles . While you are no doubt weakening our troopers ' resolve is very strong . We are not going anywhere . '' Bivens said Frein may have placed other explosive devices in the area and warned people to be very careful , especially since archery hunting season is about to begin . The self-styled survivalist may have planned the ambush and retreat for months or years , police have said . The search area is a wooded area around the border of Pike and Monroe counties . The area is not far from Frein 's family home in Canadensis , in the Pocono Mountains . The suspect has the advantage of knowing the terrain where he is hidden , officials said . Poring through a variety of clues . Last week , police said a review of a computer hard drive used by Frein showed he planned the attack and his retreat into the woods for a couple of years . The hard drive which Frein had access to indicated extensive Internet research on topics such as `` how to avoid police manhunts , use of various law enforcement technologies and skills related to survival , '' Bivens said . Police also were able to track Frein through his cell phone when he called his parents one time earlier this month , a federal law enforcement official told CNN . Frein hung up after one ring , the source said . The search has yielded an empty pack of Serbian cigarettes , Bivens said . Frein claims to have fought with Serbians in Africa and has studied Russian and Serbian languages , according to the FBI , which last week named him one of its Ten Most Wanted fugitives . Soiled adult diapers were also found , perhaps used by Frein to stay in a stationary position for long periods of time . Authorities have said that Frein hated law enforcement and that they believe that he 's solely focused on hurting more officers but not civilians . `` I do think that we have significantly degraded his ability ... to adapt , '' Bivens said Tuesday . Who is Eric Frein ?
Discovery of two pipe bomb confirms Eric Matthew Frein 's presence in wooded area , investigator says . Suspect may have been spotted within the past 24 hours . He is being sought in the death of Cpl . Byron Dickson in a September 12 ambush .