After a seven-week manhunt, Frein, 31, was captured Oct. 30 and arraigned the next day on charges including murder and attempted murder. One of the new terrorism charges accuses him of trying to affect the conduct of a government. The other accuses him of trying to influence the policy of a government by intimidation or coercion.
Officials have said Frein staged an ambush-style shooting outside a state police barracks in Blooming Grove, Pa., on Sept. 12. Cpl. Bryon Dickson, 38, was killed. Trooper Alex Douglass, 31, was critically wounded.
In an amended criminal complaint filed Thursday, police said that while being interviewed after his arrest, Frein said that "he wanted to make a change [in government] and that voting was insufficient to do so, because there was no one worth voting for."
Frein also said that shooting the troopers was an effort to make that change and that the fatal shooting was an assassination, the complaint says.
Additionally, the complaint says police found a letter addressed to "Mom and Dad" on a thumb drive belonging to Frein. The letter laments the state of the country and says that only "another revolution can get us back the liberties we once had."
"The time seems right for a spark to ignite a fire in the hearts of men," the letter says. "What I have done has not been done before and it felt like it was worth a try."
The file was created Dec. 29 and last accessed Oct. 6, while Frein was on the run, the complaint says.
According to court documents, Frein had a laptop and surfed the Internet even as hundreds of law enforcement officials scoured the heavily wooded area around his home in Canadensis for weeks. It was one of the largest manhunts in Pennsylvania history. Frein ended up being arrested near an abandoned airport hangar, about 33 miles from the shooting scene.
"I tried my best to do this thing without getting identified, but if you are reading this then I was not successful," the letter quoted in the complaint says.
Frein, who faces the death penalty, is being held without bail. His next court date is scheduled for Dec. 9.
Times staff writer Matt Pearce contributed to this report.