A Wisconsin jury Tuesday ordered a conspiracy theorist who claimed the grieving father of a victim of the 2012 Sandy Hook Elementary School massacre had fabricated his son's death certificate to pay the father $450,000.

A judge had ruled in June that James Fetzer, co-author of the book "Nobody Died at Sandy Hook," had defamed Leonard Pozner, father of Noah, 6, the youngest victim of the December 2012 mass shooting, by falsely claiming that Pozner had fabricated copies of his son's death certificate.

James Fetzer, a professor emeritus from the University of Minnesota Duluth, now lives in Wisconsin. Joey Mcleister / Star Tribune via Getty Images

The claim was made by the retired professor in his book, which argued that the Newtown, Connecticut, mass shooting — which left 20 first-graders and six staff members dead — never happened and was instead a hoax staged by the federal government in an effort to pass stricter gun laws.

A Dane County jury deliberated for almost four hours before slapping Fetzer with the $450,000 fine, the Wisconsin State Journal reported. Fetzer called the amount "absurd" and vowed to appeal, the newspaper reported.

In a statement published by the newspaper, Pozner thanked the jury "for recognizing the pain and terror that Mr. Fetzer has purposefully inflicted on me and on other victims of these horrific mass casualty events."

"Mr. Fetzer has the right to believe that Sandy Hook never happened,” Pozner said. “He has the right to express his ignorance. This award, however, further illustrates the difference between the right of people like Mr. Fetzer to be wrong and the right of victims like myself and my child to be free from defamation, free from harassment and free from the intentional infliction of terror.”

Noah Pozner Uncredited / AP

"Nobody Died at Sandy Hook" was pulled from bookshelves in June and the publisher, Moon Rock Books, has apologized to the Pozner family.

The book's co-author, Mike Palacek, reached an undisclosed settlement with Pozner last month.

Pozner has devoted years to quelling hoaxers who have harassed him and has said he has received death threats over their claims that he is a crisis actor and that his son was never real.

To push back against deniers, he has released Noah's birth certificate, medical records and report cards to the public and has had DNA samples taken to prove Noah is his son.

He and the families of seven other Sandy Hook victims are also pursuing legal action against Infowars owner Alex Jones, who has disseminated similar false claims about the mass shooting.