Richard Hyercyzk, 54, pleaded guilty Thursday to a single count of mailing a threatening letter, the U.S. attorney's office said. He faces up to five years in prison when he is sentenced.
Federal prosecutors described Hyercyzk as cooperative and said he is not a danger to others or a flight risk. He was allowed to remain free on his own recognizance pending sentencing.
Hyercyzk, a draftsman, is also an expert on lichens, common but unusual fungi that live in partnership with a species that can carry out photosynthesis, the Chicago Tribune reported. Neighbors in the Garfield Ridge neighborhood knew him as an eccentric who leads nature walks in the city.
But Hyercyzk admitted Thursday he sent letters threatening police officers with violence.
Federal prosecutors quoted from one letter that began "Dear Cougar Killers [aka Chicago PIG Police]."
Other threats included:
-- "Prepare to DIE like the Cougar you killed. On May 4th at your St. Jude Memorial March several PIGS will be shot by snipers";
-- "BURN down the Daley house in Michigan"; and
-- "Kill any Police Officer, where ever they are found, like they killed the Cougar."
The investigation by the Chicago Joint Terrorism Task Force began in 2003 and ended a decade later.