Richard Hyerczyk, 54, was charged last week in federal court. The cougar was shot in April 2008. The matter sparked debate, with some saying officers should have tranquilized the cougar instead.
Prosecutors say the threatening letters were sent a short time later. But according to investigators, they weren't the first from Hyercyzyk. They say he has a history of sending threatening letters stretching from November 2003 to December 2012.
"Mr. Hyercyzk was identified as a suspect who had sent over 90 threatening and harassing letters to individuals, entities, private officials, public officials, schools, religious institutions all over the Chicago area," said Chris Veatch, Assistant U.S. Attorney.
Prosecutors say one of those letters included threats to burn former Mayor Richard Daley's home in Michigan. There was a suspicious fire at a neighboring house.