CHICAGO (STMW) — An angry animal rights activist who threatened to avenge the police shooting of a wild cougar in Chicago by torching Mayor Richard M. Daley’s vacation home was sentenced to 27 months in prison Wednesday.

Rich Hyerczyk, 54, wrote 90 threatening letters to politicians, schools and religious institutions, including one to Daley that included the line “F – – – your dead son.”

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U.S. District Judge Gary Feinerman called Hyerczyk’s crimes “unbelievably cold-blooded.”

For more than five years after Chicago Police shot the big cat as it prowled the streets of Roscoe Village, the identity of the anonymous letter writer remained a mystery.

But in January, Hyerczyk, a lanky Southwest Side botanist, finally admitted he was behind the campaign of threats.

His plea deal with prosecutors left unresolved who actually lit an April 24, 2008, fire that spared Daley’s Michigan lakefront retreat but destroyed a neighbor’s multimillion-dollar home. But Hyerczyk admitted he’d mailed an anonymous letter just three days earlier in which he vowed to “BURN down the Daley house in Michigan.”

Prosecutors did not refer to the blaze in sentencing papers, but asked Feinerman to impose a sentence of 2 to 2 1/2 years for Hyerczyk, saying his crimes caused “terror.”

Hyerczyk’s letters contained racist and anti-Semitic threats, and some, including one sent to Brookfield Zoo, contained white powder that was meant to scare recipients, prosecutors said.

Investigators also found evidence he’d searched for child porn on his computer, they alleged.

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But Hyerczyk’s lawyer asked for a sentence of probation, arguing Hyerczyk was mentally ill, suffering from obsessive personality disorder. It was “stupidity” that motivated him, because he was “under tremendous stress with the killing of animals and humans,” his attorney Michael Vitale wrote.

In one of his threatening letters Hyerczyk, of the 5200 block of South Natoma, warned that police should “Prepare to DIE like the Cougar you killed.”

The 124-pound cougar whose death sparked the threats likely traveled more than 1,000 miles from South Dakota before police, fearing for public safety, shot it six times a block from Audubon Elementary School in a case that made front page news on April 14, 2008.

A week later, Hyerczyk mailed multiple copies of a letter in which he said he’d kill “PIGS” at the annual St. Jude Memorial march and made threats against police officers’ “wives” and “children.”

Sources said his letter to Daley included rants against the former mayor, his wife Maggie, his son Patrick, his daughters Nora and Lally, and even his son Kevin, who died of spina bifida 27 years ago when he was just 33 months old.

Daley at the time called it “really hurtful.”

Hyerczyk, an unmarried St. Xavier University graduate, works at a La Grange Park molding company and has an interest in lichen that led him to found the Chicago Lichenological Society, records show. He’s taught natural history and botany classes at the Field Museum, Morton Arboretum, McHenry County College and Chicago Botanic Garden.

Though investigators believe his threats began with a letter to Brookfield Zoo, the unsolved arson next door to Daley’s home in 2008 remains the only case in which there’s any evidence that anyone may have followed up on one of Hyerczyk’s threats, authorities say.

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(Source: Sun-Times Media Wire © Chicago Sun-Times 2014. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)