The single-page letter refers to the boy as a nuisance, before suggesting the family move away or euthanize the child.
"The part about donating his un-retarded body parts to science because he's no good for anything else, that made me wanna puke," said mom Karla Begley, who said she is still in disbelief at the hatred targeting her son Max, who was diagnosed with severe autism just before he turned 2.
A neighbor anonymously mailed the letter to the boy's grandmother, complaining about the 13-year-old's behavior, saying things like, "that noise he makes when he is outside is dreadful, it scares the hell out of my normal children," signing it, "Sincerely, one pissed off mother."
"I really don't think it was a mother because a mother could never, never write that stuff about a child," Begley said.
Max stays at his grandmother's home in Newcastle a couple days a week during the summer. The family says they have no clue who may have been behind the letter since they haven't had many negative experiences in the neighborhood. There was only one incident four years ago when Max threw a plastic ball over a neighbors fence.
"It came back shredded... like somebody cut it up into ribbons and threw it back," said Begley.
When it comes to the letter, Durham police are investigating and have forwarded the note to the Crown Attorney's Office.
"Obviously it's a concern for anyone that would read it... for us though; it takes that next level in terms of determining whether there is an offense in here or not," said Dave Selby, Durham Regional Police spokesperson.
"I hope the police do find them and I hope they release his name to the neighborhood because the neighborhood's very upset," said neighbor Angela Palantzas.
Max doesn't know about the letter, but his family say they appreciate the show of support they've received in person and online.
Police say they'll determine their next move when they decide if the letter warrants any charges.
