The letter was sent last Friday to the grandmother of a 13-year-old autistic boy in Newcastle, Ont., telling her to move or have the teenager euthanized.
It was signed by someone claiming to be a mother in the area who was upset about noises the boy made when he was outside.
But Wade Huntley from West Jordan, Utah, who calls himself "the proud father of a son with autism," says he cannot avoid addressing the issue and says $100 is all he can afford.
In making his offer via a comment posted on Toronto Star late Wednesday, he says the author "does not deserve anonymity after the hateful things that she said."
On his website, http://www.avoiceformyson.com, Huntley calls the author a "coward" who has chosen to hide behind anonymity.
"Given the hurtful things that you have said, I doubt it will require any reward for someone to reveal who you are."
Meanwhile, the family of the boy has received offers from people to pay their bills, send them on holiday or give them gift cards.
Police have launched a criminal investigation but have said the letter does not constitute a hate crime.
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