Pennsylvania cop shooter's rifle found, police say (PHOTOS)

NORTHEASTERN PENNSYLVANIA (CNN) -- Authorities hunting suspected cop-killer Eric Matthew Frein say they discovered an AK-47 rifle, some magazines and a small bag of ammo in the northeastern Pennsylvania woods where they believe he was hiding.

"We believe we are closing in on him," State Police Lt. Col. George Bivens told reporters on Sunday.

Tracking dogs and searchers are indicating "we're on the right trail," he added, and investigators are "confident he's in (the) general area."

Frein, 31, is wanted in connection with the killing of one state police officer and the shooting of another officer that occurred September 12 outside the Pennsylvania State Police barracks in Blooming Grove.

Frein had been planning the ambush for months or possibly years, authorities said.

Investigators are "making progress," they said, referring to the items they discovered which they believe Frein abandoned or hid. Police have received hundreds of tips, Bivens said.

As to the rifle that was found, it was positioned in such a way that it could be seen, and the items were partially concealed, Bivens said.

"Frein obviously knows we're there" searching, Bivens added.

Up to 400 law enforcement officers are searching for Frein, including members of the FBI, the U.S. Marshals Service and the Bureau of Alcohol, Tobacco, Firearms and Explosives.

They are combing about 200 to 250 square miles of wooded area not far from Frein's family home in Canadensis -- about 20 miles from where Frein alleged shot state police officers.

Hunters should avoid the thick woods, Bivens urged. Schools in the areas have canceled classes.

Anyone with information or images they believe might be helpful should call 911 or contact law enforcement, Bivens stressed.

Frein has extensive training as a marksman and is a survivalist capable of living in the woods, authorities say, and they're worried he'll try to hurt more officers.

"We have every reason to believe Frein is focused on law enforcement," said Bivens, who reiterated that Frein "targeted police specifically."

"I am convinced that Frein has engaged in a personal battle with law enforcement, specifically the Pennsylvania State Police, and will likely stay focused on that fight," he said.

Bivens told reporters that Frein has "had every opportunity to harm others," though Bivens didn't go into detail about how police have determined that.

Bivens also warned that anyone who helps Frein will be charged accordingly.