Authorities hunting a survivalist and suspected cop killer in the rugged woods of eastern Pennsylvania say they believe they are closing in on him and have brought in a 6.5-ton armored tactical vehicle dubbed "The Rook" and outfitted with robotic video cameras to assist in a search now entering its 12th day.

Lt. Col. George Bivens told a press conference Wednesday that officers believe they spotted 31-year-old Eric Frein, who is charged with killing one trooper and wounding another, as recently as Tuesday. However the distance and extremely rugged terrain separating the officers from Frein in each sighting meant "he has had the ability to disappear," Bivens told reporters.

Police found empty packs of Serbian-branded cigarettes and soiled diapers believed to have been left by the suspect, Bivens said, helping to cement authorities' belief they are close to him. Police believe Frein is using diapers so he can remain stationary for long periods of time, Fox News reports.

The massive ongoing search now includes a 13,000-pound Rook armored vehicle. The armored critical incident vehicle produced by Ring Power Tactical Solutions allows officers to gain entry to the second story of a house without a ladder or to deploy snipers to rooftops.