HARTFORD, CONN. (AP) - The parents of one of the 20 children killed in the Sandy Hook Elementary School shooting are asking Facebook founder Mark Zuckerberg to remove hateful and harassing comments posted by conspiracy theorists who say the shooting never happened.

Leonard Pozner and Veronique De La Rosa wrote Mr Zuckerberg a letter published on July 25 in The Guardian. Their 6-year-old son, Noah, died in the December 2012 Newtown shooting, which also claimed the lives of six educators.

Mr Pozner and Ms De La Rosa say they and other relatives of mass shooting victims have beenharassed and threatened on social media and in person by people who claim the shootings were government hoaxes and the victims were actors.

"Our families are in danger as a direct result of the hundreds of thousands of people who see and believe the lies and hate speech, which you have decided should be protected," they wrote. "We are unable to properly grieve for our baby or move on with our lives because you, arguably the most powerful man on the planet, have deemed that the attacks on us are immaterial, that providing assistance in removing threats is too cumbersome, and that our lives are less important than providing a safe haven for hate."

Last year, a Florida woman who threatened Mr Pozner was sentenced to five months in prison. Authorities said Lucy Richards made voicemail and email threats to Mr Pozner in January 2016 after viewing internet sites claiming the shooting was a hoax aimed at curtailing Americans' Second Amendment gun ownership rights. Ms Richards pleaded guilty to interstate transmission of a threat to injure.

Other parents of Sandy Hook victims and people affected by other mass shootings, including the one that killed 17 people at a Florida high school, have made similar requests of Facebook, Twitter, and other social media companies.

Mark Zuckerberg raised eyebrows in an interview with Recode last week when he said he finds denial of the Holocaust "deeply offensive" but does not believe such content should be banned from Facebook.

"What we will do," he said, "is we'll say, 'Okay, you have your page, and if you're not trying to organize harm against someone, or attacking someone, then you can put up that content on your page, even if people might disagree with it or find it offensive.'"

He also said in the interview that the claim the Sandy Hook shooting did not happen is false.

"I also think that going to someone who is a victim of Sandy Hook and telling them, 'Hey, no, you're a liar' - that is harassment, and we actually will take that down," Mr Zuckerberg said.

In a statement Wednesday in response to the letter by Mr Pozner and Ms De La Rosa, a Facebook spokeswoman said the company recognizes that victims of mass shootings and other tragedies are "vulnerable to offensive and incendiary comments."

"Although we do see people come together on Facebook in very positive ways around tragedies, some of what we see is truly abhorrent and represents the worst of the internet and humanity," the statement said. "We don't allow people to mock, harass, or bully the victims of tragedies. This includes the types of claims in the letter that victims are crisis actors. We also don't allow people to celebrate, justify, or defend the tragedy in any way."