Families of America's gun massacre victims, including those from the Sandy Hook school shooting and the latest rampage in Orlando, are being stalked by conspiracy theorists and "gun truthers" who claim the atrocities never happened.

Grieving parents from the Sandy Hook massacre are being told their children never died or never even existed.

The harassment started within days of the shooting, when a young man armed with a military-style assault rifle ran amok at Sandy Hook elementary school in Connecticut, USA, in December 2012, killing 20 first graders and six teachers.

It continues to this day.

"F*** you!! Your child never died at Sandy Hook," is one among thousands of online posts that Lenny and Veronique Pozner have had to deal with as they mourn their six-year-old son Noah.

"Where's Noah going to die next?" is another.

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Some "gun truthers" claim Sandy Hook was a government-sponsored stunt aimed at galvanising support for tougher gun laws.

"There are many conspiracies, many theories, one of which is that Noah is an actor and he's never really died and that we're all actors," Mr Pozner told Foreign Correspondent's Lisa Millar.

Unlike most bereaved parents, Lenny Pozner refuses to ignore the trolls. He dedicates himself to confronting them.

So in a country awash with conspiracy theories — 9/11, JFK, Obama's backstory — why does he bother?

"I have to absolutely defend the memory of my son — I have no choice," he said.

"I know how some of these theories build up. They don't fade away and the more time they spend online, the more accepted they become.

"The JFK conspiracy theory in the US is very accepted. Conspiracy theories erase history, they erase our memories, and how will this event (Sandy Hook) be remembered a hundred years from now?

A heart is emblazoned with crosses to commemorate the 26 Sandy Hook Elementary School shooting victims. ( Reuters: Carlo Allegri )

"So I think it's important the work that I'm doing."

Mr Pozner has founded a group called the HONR network, which aims to "bring awareness to hoaxer activity" and "prosecute those who wittingly and publicly defame, harass and emotionally abuse the victims of high-profile tragedies".

There is no criminal law to protect bereaved families from trolling, so whenever Mr Pozner and his volunteers find a video or rant attacking victims of tragedy, they alert outlets like YouTube or Facebook.

Or they go to police or other authorities and publish the complaints.

They have succeeded in removing many links to dark content, though thousands more remain.

Family receives death threats

Mr Pozner has received multiple death threats and takes precautions.

A condition of his interview with Foreign Correspondent is that his face is not shown.

The harassers are not all faceless nobodies.

Families who lost their children have been harassed online. ( Reuters: Adrees Latif )

One radio shock jock wrote of Sandy Hook: "It would take a fool not to question the motive behind it all: Is this all part of an evil pre-conditioning program?"

But Mr Pozner's highest profile adversary has been James Tracy, whose status as a Florida university professor of communications won him huge publicity when he suggested Sandy Hook was bogus.

Professor Tracy even demanded the Pozners provide proof Noah once lived, and that they were his parents.

The university sacked Professor Tracy a few months ago. He is appealing the decision.

"That was a very strong success … a very powerful statement that that sort of behaviour is not acceptable," Mr Pozner said.

"A lot of people who are conspiracy theorists throw around this freedom of speech concept. But that's not what it means — it's not protection from abusing people."

For Mr Pozner, it is impossible to let go of the past, except in the most literal sense.

He has moved interstate to an undisclosed location. Sandy Hook was too raw.

"The more time and the more distance, the less heavy it becomes," he said.

Locals frustrated tougher gun laws never eventuated

Lisa Millar, who reported extensively on the Sandy Hook shootings, returns to the town for Foreign Correspondent to tap into the mood after yet another massacre, this time in Orlando.

She finds the school is now being rebuilt — townsfolk are trying to move on.

Connecticut has now banned most assault weapons.

US president Barack Obama called for tougher gun laws in the wake of the Sandy Hook massacre. ( Reuters: Larry Downing )

But many locals are frustrated the tougher national gun laws predicted after Sandy Hook never eventuated.

And they are angered by the insidiousness of the "truthers".

"What's frustrating is that the ones who don't even own guns buy into that propaganda, the nonsense that this never happened or that it was a government false flag operation to take away people's guns," said Eric Milgram, whose daughter evaded the shooter by hiding in the bathroom.

"You know, that's just a stupid, stupid idea."

Mr Milgram has this grim advice for families of this month's Orlando killings: "Be prepared that when you speak out you will be harassed."

"These gun nuts, these extremists, these hoaxers, these nasty people, you've gone through a horrible trauma, be prepared that you're going to be harassed on social media.

"People are going to call your house, they're going to get your work phone number, they're going to threaten you, they're going to tell you that you're part of a conspiracy.

"You're going to be victimised all over again."

Honouring Noah, reported by Lisa Millar, airs on Foreign Correspondent on Tuesday, June 28 at 9.30pm on ABC TV.