A San Francisco police union has accused former domestic terrorist William Ayers, co-founder of the Weather Underground, and his wife in a 1970 bombing that killed one sergeant, the San Francisco Chronicle reports.

The union, in a letter to a conservative organization lobbying for arrests in the case, accused Ayers and wife Bernardine Dohrn of bombing a city police station.

On Feb. 16, 1970, a bomb placed on a window ledge of Park Station killed Sgt. Brian McDonnell and injured eight other officers, the Chronicle reported.

The union said it had not been in contact with investigators nor did it have new evidence, but it cited Larry Grathwohl, who works with the conservative organization America's Survival of Maryland and claims that he infiltrated Weather Underground as an FBI informant and heard Ayers confess, the Chronicle reported.

"There are irrefutable and compelling reasons to believe that Bill Ayers and his wife Bernardine Dohrn ... are largely responsible for the bombing of Park Police Station," the Feb. 24 letter reads, according to the Chronicle.

Ayers denies any involvement in the bombing and told the Chronicle in January that his accuser, Grathwohl, was a "paid dishonest person."

Ayers was once again thrust into the spotlight during last year's presidential campaign, when President Obama's ties to the radical were questioned.

Ayers is now an education professor at the University of Illinois at Chicago. Dohrn is a law professor at Northwestern University.

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