Alleged Pennsylvania cop killer Eric Frein was charged with two additional counts of terrorism after investigators found a letter to his parents declaring that only "another revolution can get us back to the liberties we once had."

Frein, 31, is charged with murdering state police Cpl. Bryon Dickson and wounding Trooper Alex Douglass in a Sept. 12 ambush on a Pennsylvania State Police barracks. A preliminary hearing had originally been scheduled for Dec. 9, but the new counts were entered Thursday in an unexpected hearing in Pike County Magisterial District Court.

The new charges — terrorism to influence the policy of government by intimidation or coercion and terrorism to affect the conduct of a government — carry maximum sentences of 40 years in prison.

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"Tension is high at the moment and the time seems right for a spark to ignite a fire in the hearts of men," says the letter investigators said they found on the hard drive of a computer . "What I have done has not been done before and it felt like it was worth a try."

The letter's writer goes on to complain: "There is so much wrong and on so many levels [that] only passing through the crucible for another revolution can get us back to the liberties we once had. I do not pretend to know what the revolution will look like or even if it would be successful."

Prosecutors have said they plan to seek the death penalty. While Frein, a self-styled survivalist and military buff, allegedly left behind a letter recounting how he picked off the two officers with rifle fire and then fled into the woods.

A count of attempted homicide was dropped in the amended complaint. The Pocono Record newspaper reported Thursday that an attorney for Frein's family complained that he'd been denied access to Frein shortly after his arrest. The lawyer, James Swetz, told the newspaper that Frein could make a reasonable argument to strike his statements to police because they were made without counsel present. It couldn't be determined whether that argument was related to the new complaint.

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Eric Frein appeared on video sitting in orange jumpsuit. His two attorneys were standing behind him — Eric Deabill (@ericdeabill) November 13, 2014

— M. Alex Johnson