The author of the book "Nobody Died at Sandy Hook" must pay the father of one of the shooting's victims more than NZ$700,000.
On Tuesday a Wisconsin jury ordered James Fetzer to pay Leonard Pozner NZ$715,819 (US$450,000).
Fetzer's book claims the horrific shooting never occurred and was orchestrated by the Obama administration in order to enact tighter gun restrictions.
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Pozner's six-year-old son Noah was the youngest of 26 victims who died in the 2012 shooting.
He filed a defamation claim against Fetzer, reports CBS. Pozner says the book caused him to receive hateful messages and death threats.
"It causes people to believe that I lied about my son's death, that my son didn't die, and that I'm somehow doing that for some other reasons," said Pozner.
When Fetzer took the stand on Tuesday the retired professor attempted to argue his book is not defamatory as the statements in it are true.
The judge would not allow him to argue the legitimacy of false statements, reports CBS.
Fetzer said the amount of the damages was "absurd" and plans to appeal.