— Law enforcement officials have reported sightings of Eric Matthew Frein, but haven't been close enough to apprehend the suspected police killer, said state police Lt. Col. George Bivens during a news conference Wednesday.

Officers have seen Frein from a "significant distance" but apprehending him has been difficult due to the rugged, rocky terrain, dense vegetation and numerous caves in the area of Barrett and Price townships in Monroe County, police said.

"We believe we are in the right area. It is only a matter of time before we catch him," Bivens said.

The officer added, "I want to tell him it's time to surrender."

Authorities will not go away until Frein is apprehended, Bivens said.

"We're here for the long run. I'm optimistic this will end as soon as possible," Bivens said, noting that lethal force could be used if Frein doesn't "actively surrender."

Anyone who sees Frein or has any information is urged to call 1-866-326-7256.

Frein is accused of fatally shooting state police Cpl. Bryon Dickson II, 38, outside the barracks in Blooming Grove Township on Sept. 12. Trooper Alex Douglass, 31, also was shot but is recovering.

Bevins said police have used "tremendous restraint" during the sightings and they want to apprehend the suspect alive.

Police did not fire any shots during the sightings, the officer said.

Authorities believe Frein, described as a survivalist, traveled 15 to 20 miles from the barracks area to where they believe he is now in Monroe County, near his parents home.

Police said they still believe Frein acted alone, but anyone who abets him would be charged.

Bivens said that when the sightings occurred Frein appeared to be dressed in black clothing with a hood.

The officer said, "In some ways, I think this is a game to (Frein)." He said the suspect has come out of hiding, apparently to check on police perimeters.

Frein has been far enough away to elude capture, but close enough to be identified, Bivens said.

Trackers also have found Serbian style cigarette packets and soiled diapers they believe belong to the suspect.

Frein was a member of an eastern Pennsylvania military simulation group, where participants assumed the roles of soldiers from eastern European countries in the Cold War era, according to police.

The search is concentrated in a two- to three-mile area of Barrett and Price townships, but the entire investigation spans multiple states, Bivens said.

The officer thanked the community members in the search area for their patience and understanding.

The police presence, and that of a suspected killer, "changes the way people live and we're trying to be as accommodating as possible," Bivens said.

Police are asking people to stay out of woodlands in the area, including the Delaware State Forest.

The reward for the capture of Frein is $175,000.