Noah Pozner was reluctant to go to school that day. A mischievous little boy, who had celebrated his sixth birthday three weeks earlier, he stayed in bed too long and dragged his feet getting ready. “I said to him: ‘Come on, Noah, we gotta get moving,” his father, Leonard (also known as Lenny) recalls, having thought about the morning of 14 December 2012 so often he can almost talk about it mechanically. But the drive was fun: Noah, his twin sister, Arielle, and older sister, Sophia, listened to Gangnam Style, one of Noah’s favourite songs. Noah always sat in the back seat and Leonard tickled his ankle as he drove along. At school, Noah jumped out, his backpack in one hand, his jacket in the other. He was wearing a Batman shirt and Spider-Man trainers. “I said: ‘I love you, have a great day,’ and that was the last thing I ever said to him,” says Pozner. After all, he adds, “Not even Batman could have stopped an AR-15.”

Noah was the youngest victim of the Sandy Hook elementary school shooting, murdered about half an hour after his father dropped him off. A sweet-faced, big-eyed, brown-haired boy, his tiny body took multiple bullets. His jaw was blown off, as was his left hand, and his beloved Batman shirt was soaked with blood. For his funeral, his mother, Veronique, insisted he have an open casket.

“I want the world to see what they did to my baby,” she said at the time.

Today, Pozner tries to look on the bright side. “I could have lost three kids that day because the other two were in rooms adjacent to Noah’s classroom. They were all in the shooter’s footprint.”

Even in a country all too used to mass shootings, the merciless killing in Newtown, Connecticut of 20 six- and seven-year-olds, along with six of the school’s employees, retains a terrible hold on the US’s imagination, gripping the memory after too many other shootings have faded away. For most, it is too horrible to mention without a shudder. But for a tenacious few, it is too horrible to believe, and soon after Noah was killed, when Pozner thought he had already seen the worst of humanity, he came into contact with the latter group.

Just days after the massacre, when the US was still reeling from the tragedy, and Pozner himself was, he says, “pretty much in a catatonic state”, the theories started spreading: Sandy Hook had never happened, it was staged by actors, the children had never existed, it was a ruse by President Obama/the anti-gun movement/the “New World Order global elitists”. So-called Sandy Hook truthers – Pozner prefers the term hoaxer – pored over photos of the families and children on social media, triumphantly pointing to any visual similarities they could find between the dead children and living ones. The families were harassed by hoaxers, online and off, insisting that they stop their fake grieving. When Pozner roused himself from his catatonic grief to post photos of Noah online, hoaxers would leave comments: “Fake kid”, “Didn’t die”, “Fucking liar”.

Pozner and I speak by phone. His voice is sad and heavy, but he talks easily. He and Veronique were separated at the time of the shooting, sharing custody of their kids. They reunited in the wake of Noah’s death, but that soon fell apart. Pozner has moved half a dozen times since Noah’s death, always staying near Veronique and their daughters, and is moving again soon after our interview. Partly, this is because each move is a new start, “and I need that sometimes”, he says. But it is also because he has to keep ahead of the people who, for the past five years, have been sending him death threats, purely because his son was killed in Sandy Hook.

Arielle Pozner, Noah’s sister, at Noah’s grave. Photograph: Courtesy Leonard Pozner

The week before our interview, a judge issued a warrant for the arrest of Lucy Richards. She is alleged to have sent messages to Pozner, including one that read: “Death is coming to you real soon and nothing you can do about it.” That was bad, Pozner agrees, but not necessarily the most unsettling. After all, others have put photos of his house on the web and reported him to child-protection services. “This is the world I deal with now,” says Pozner.

I started corresponding with Pozner in September 2016, after I read an article about him in a US magazine. He saw me tweeting about it and got in touch. I was surprised at how grateful he seemed for my sympathy about Noah. But then I remembered that he had spent countless hours dealing with people telling him that he should exhume his son’s corpse to prove its existence. I told Pozner that, having lost someone in 9/11, I understood how painful it is for people to use your tragedy for their own self-indulgent obsession. He thanked me again.

Pozner himself used to be into conspiracy theories. When he lived in Connecticut, he often had to commute to New York and would listen to rightwing radio hosts such as Alex Jones and Michael Savage on the long drives. “I’m self-employed, an entrepreneur. I was always looking for more information so I could get an edge on the next guy, to get a better idea of the geopolitical perspective,” Pozner says. Once he got used to Jones’s “raspy voice” he liked him especially: “Alex Jones appears to think out of the box. He’s entertaining.”

Arguably, more than anyone, Jones is responsible for spreading the theory that the Sandy Hook massacre was fake. His radio shows and website, InfoWars.com, have an audience of more than eight million, and they specialise in the kind of conspiracies that had intrigued Pozner: was 9/11 an inside job? Was the US government involved in the Oklahoma City bombing?

On 27 January 2013, Jones told his audience: “In the last month and a half, I have not come out and said this was clearly a staged event. Unfortunately, evidence is beginning to come out that points more and more in that direction.”

“I wasn’t very verbal at that point, but I managed to send Alex Jones an email,” says Pozner. He wrote: “Haven’t we had our share of pain and suffering? I used to enjoy listening to your shows. Now I feel that your type of show created these hateful people and they need to be reeled in!”

He got a reply from Jones’s assistant, who said: “Alex has no doubt this was a real tragedy.” But Jones’ thinking seemed to change. In 2015, he told his audience: “Sandy Hook is synthetic, completely fake, with actors; in my view, manufactured. I couldn’t believe it at first. I knew they had actors there, clearly, but I thought they killed some real kids, and it just shows how bold they are, that they clearly used actors.”

The year before InfoWars.com ran a story headlined: “FBI says no one killed at Sandy Hook.”

The US has a long history of conspiracy theories. The majority of Americans today don’t believe Lee Harvey Oswald acted alone in killing John F Kennedy. Pozner says the Sandy Hook hoaxers are different because previously there were “no targets”. I say this isn’t quite right: John F Kennedy Jr found conspiracies about his father’s assassination so painful, he would leave the room when people started swapping them over the dinner table, and those of us who knew people who died in 9/11 will have all had similar experiences. He clarifies and says what he means is that the most hardcore conspiracy theorists can now, thanks to the internet, easily track down and personally target those affected by the tragedy. But an even bigger change is that those who are promoting the most crackpot of theories are no longer relegated to the weird, dark fringe. Rather, they are swimming in the mainstream, thanks to one man in particular.

Police lead children from the Sandy Hook school in December 2012. Photograph: Shannon Hicks/AP

In 2015, Donald Trump went on to Alex Jones’s show for a half-hour interview. At the end of the show, Trump said to the man who once claimed the government is putting chemicals into the water to turn people gay and stop them from having children: “I just want to finish by saying your reputation’s amazing. I will not let you down, you will be very, very impressed, I hope. And I think we’ll be speaking a lot ... You’ll be very proud of our country.”

Trump is very comfortable with conspiracy theorists. Steve Bannon, of course, made his name with Breitbart News, the conservative news website known for its hyped-up reporting of conspiracies. His original choice for national security adviser, General Mike Flynn, was notorious for tweeting conspiracy theories, such as that Hillary Clinton was involved with child-sex trafficking, and he claimed the Democrats wanted to impose sharia law in Florida. His adviser, Roger Stone, has claimed that Chelsea Clinton had multiple plastic surgeries as a teenager to disguise her true paternity. Trump’s deputy campaign manager, David Bossie, made a 2008 documentary, Hillary: the Movie, which reported the allegation, among other things, that Hillary Clinton had the cat of a woman who made claims of sexual harassment against Bill Clinton killed.

Mike Cernovich is another conspiracy theorist who, by rights, should only be known among the most misogynistic and angry. He was one of those responsible for spreading the so-called “pizzagate” story, which claimed that Hillary Clinton and other top-level Democrats were running a child sex ring out of a pizza parlour in DC. In December, a man fired a rifle inside the restaurant, determined to find the alleged child sex slaves he had read about online. In early April, he published a blog claiming the former national security adviser Susan Rice had engaged in illegal surveillance activity. In fact, his blog revealed nothing more than that there were longstanding and well-known concerns about surveillance. Nonetheless, he received an endorsement from Trump’s counsellor, Kellyanne Conway, and Donald Trump Jr tweeted: “Congrats to @Cernovich for breaking the #SusanRice story. In a long gone time of unbiased journalism he’d win the Pulitzer, but not today!”

And then there is Trump himself, a man whose greatest political triumph before winning the presidency was promoting the “birther” conspiracy theory, which revealed only Trump’s apparent inability to believe black people can be born in the US. In the months since he was inaugurated, he has merrily promoted conspiracy theories with the enthusiasm of a devoted InfoWars fan. These have included: 3m votes in the election were cast illegally; the media is covering up acts of terrorism; Obama tapped his phone while president. Then there are his longstanding theories about vaccinations (“AUTISM”) and climate change (“a hoax”).

Earlier this year, the Newtown school board sent Trump a letter, asking him to denounce Alex Jones and the other Sandy Hook hoaxers, and to state definitively that Sandy Hook happened: “Jones repeatedly tells his listeners and viewers that he has your ears and your respect. He brags about how you called him after your victory in November. He continues to hurt the memories of those lost, the ability of those left behind to heal,” the school’s board wrote. Two months on, they have yet to receive a response.

Pozner says this doesn’t bother him, not really: “I don’t want to have anything to do with Donald Trump or the crowd he surrounds himself with.”

I ask how he feels about stories such as pizzagate going mainstream. “It feels like I’ve been proven right – hoaxers need to be handled, not ignored. It’s like a brushfire: you need to shape it and direct it. But if you leave it alone, it will burn down your forest, and it has reached all the way to the White House,” he says.

Since 2014, when he started to engage with the world again, Pozner has been trying to shape his brushfire. At first, he tried to engage with the hoaxers and some, he found, were young mothers who simply couldn’t allow themselves to believe someone could look a six-year-old in the eyes and shoot them in the head. Pozner had a lot of sympathy with them, as he felt the same way. Others, he says, are “just kids who get sucked into this world and they feel more confident about themselves, more certain, and they feed off the echo chamber of info, usually from websites. And they get taken in, hook, line and sinker.” One such hoaxer recently posted a comment beneath one of the online tribute videos to Noah: “You criminals need to be boiled in faeces.”

Pozner realised quickly that there was no point in arguing with these hoaxers, so instead he attacks through copyright law. Every day, he Googles Noah’s name to see if anyone has put up a photo or video of his son without his permission and, if so, he files copyright claims. Thanks to Pozner’s dedication and experience as an IT consultant, he has scrubbed Noah’s search results of toxic-hoaxer content. He has sued other hoaxers for invasion of privacy, and successfully petitioned a Florida university to fire a professor, James Tracy, for hoaxing. (Tracy has sued for wrongful termination.) He also founded the HONR Network, which helps grieving families deal with online abuse, and it lobbies YouTube, Google and Facebook to stop hosting such abuse. It has also turned the tactics of some of the most persistent hoaxers on the hoaxers themselves, demanding they answer endless banal questions about their personal lives as if trying to catch them out, just as they do of the Sandy Hook families. Veronique, he says, supports his work, but she doesn’t have the stomach for it herself. I ask if his campaign has been a means for him to channel his grief and anger about the death of his son.

“It may appear that way, but it’s not a healing journey – it’s taxing and draining, and I don’t think there’s a healing aspect to being drained this way. Maybe [I do this] because I was bullied when I was younger, so I have a low tolerance to being pushed around. But I never imagined I’d have to fight for my child’s legacy. I never imagined life without any of the children at all.”

Pozner says that, if he hadn’t lost Noah, he might well have believed the pizzagate conspiracy: “I would not have been as immediately dismissive of it, that’s for sure. History books will refer to this period as a time of mass delusion. We weren’t prepared for the internet. We thought the internet would bring all these wonderful things, such as research, medicine, science, an accelerated society of good. But all we did was hold up a mirror to society and we saw how angry, sick and hateful humans can be.”

So what can we do, I ask, now that more of us are realising we can’t just ignore these people?

“It’s too late, and things have gone too far. The whole Amazon is on fire. When I was dealing with these people in 2014 and 15, you could utilise their stories and turn them around. I don’t know if you can even do that now,” he says. “Lawmakers don’t know how to deal with this. Police don’t know how to police the internet, they haven’t been trained, they just tell you to turn off the computer. And people who do police the internet, they are looking for credit card scams worth millions of dollars. For 4Chan trolls, this is their playground.”

He pauses for a moment: “I used to be able to change the channel when stories about these kinds of people were on. I now don’t have the luxury to do that, and when I lost Noah, I woke up and realised that people who spread these stories are more interested in propagating fear than getting at the truth. And the human cost of that is phenomenal.”