Five days after the Parsons Green bombing in September 2017, a Facebook post went viral. In it, a Facebook group called “The Crisis Actor” claimed that an unidentified victim of the attack was in fact The Office actress Nora Kirkpatrick. “She had time to pose for photo opportunities with the waiting media looking like she just walked out of a beauty salon,” read the caption on a photo of the red-headed victim, whose ear was bandaged after the attack.

The act of terrorism was declared just that – an act, forcing Kirkpatrick to explain on social media that she was in LA shooting a movie on the day of the bombing (and also, that she now has blonde hair). Still, YouTube videos spreading the theory came thick and fast. “‘Wall of fire’ and Ginge hasn’t a singe, if your friends and family fall for this shit give em a fuckin slap,” reads one YouTube comment about the same victim.

As rude and callous as they are, there is nothing extraordinary about these social media posts. After every major tragedy, conspiracy theorists inevitably claim that it was a “false flag” – a fake event planned by the government or military to push forward their own agenda. But thanks to the internet, these rumours spread rapidly, and conspiracy theorists have a direct line to the victims of attacks, who they think are “crisis actors”. With a few clicks they can stalk, harass, and abuse victims who they believe were paid by the government to lie.

“It’s really changed the way that I feel towards social media, when you receive that much hate after going through a very traumatic experience,” says Emma Stevie, a 27-year-old who was a passenger on the Parsons Green tube that was bombed (she is not the red-haired woman, who remains unidentified). After Emma gave a television interview about her experiences, truthers found her on social media and claimed she was a crisis actor. Their justification was that she works in the beauty industry and has her own blog and YouTube channel. Some accused her of being part of the illuminati. Others sent her threats.

“I got rape threats; I got told that I should be given to Isis so they can do terrible things to me... I couldn’t sleep that night," Emma says. "When you’ve received hundreds and hundreds of trolling messages from people that want bad things to happen to you, you do look over your shoulder when you’re walking around.” At the time of writing, there are 266 results if you search “Emma Stevie crisis actor” on YouTube. “Wonder how much this bitch got paid for lying?﻿” reads a comment on one of the most popular. Although her Twitter notifications have slowed down, Emma still receives “nasty comments” at least once a day.

Although Emma’s experiences are regrettably not unusual, there is something different about the trolls’ narrative in this case. The most infamous truther movement emerged after the Sandy Hook school shooting in 2012, when conspiracy theorists attacked the parents of children who had died in the attack, claiming that their children had never existed in the first place. Many truthers are gun-activists who believe American shootings are orchestrated by the government in order to push through tighter gun control. Many gun activists are also now claiming the tragic events in Las Vegas this week were a hoax.

Parsons Green truthers are different. They’re British, anti-establishment, and notably more left-wing. A gun activist clearly has an ulterior motive in claiming shootings are false flags. But what makes a British citizen claim terrorist attacks in their country are faked?

“The post was meant to stimulate debate,” says the man behind The Crisis Actor Facebook page, who is aged over 50 and a public service worker from Edinburgh, but otherwise wishes to remain anonymous. “Some people believe that all terrorist attacks are orchestrated by state security to keep the population permanently on edge.”

The man behind the page says he is left wing, and he runs two other “socialist” Facebook pages with a combined following of 300,000 people. After the fact-checking website Snopes poked holes in his viral meme, he deleted it and now says he doesn’t believe that the red-headed victim was a crisis actor. Instead, he now believes “that government agent provocateurs are infiltrating and handling terrorists”, and the Parsons Green attacker was potentially one of these men incited by the government.

It is his belief – one shared by the 10,000 followers of The Crisis Actor Facebook page – that the government orchestrate terrorist attacks in order to push through a greater military presence and to justify restrictions on our online freedoms. Similarly, after the 7 July 2005 bombings in London, some bloggers claimed they were faked to drum up anti-Muslim sentiment.

“I just have to feel sorry for them, I’m sorry you’re so deluded and I’m sorry that you believe that I'm an actor, but one day this could happen to you,” says Emma. Trolls who believe she was acting claim that her response to terror was unbelievable, but Emma points out that you never know how you’ll react until it happens to you. “Stress does very strange things to you, it makes you glaze over, it makes you go into a weird present-but-not-present state of survival, which means no emotion for me at all.”

Although many Parsons Green conspiracy theorists claim the government are trying to push through surveillance laws, many others don’t feel the need to justify or explain their beliefs. There are many truthers who believe in multiple false flags, automatically assuming that all tragic news is faked. “I find it very hard to believe there is any terrorists anywhere [sic],” reads a YouTube comment on a Parsons Green conspiracy video. What motivates someone to immediately cry conspiracy after a tragedy?

“Two important aspects of our psychology are our ability to spot patterns, and our resistance to being duped,” says Dr Robert Brotherton, author of Suspicious Minds: Why We Believe Conspiracy Theories. “When we go looking for some pattern we're great at finding clues that seem to confirm it.”

Brotherton explains that truthers are experiencing “motivated reasoning”, in that people who are eager to see a conspiracy find it easy to find signs of a conspiracy. “When you’re not motivated to see a conspiracy, it’s easy to call the conspiracy theorists crazy. And when you do see a conspiracy, it’s probably going to be one that fits with your wider worldview. So right-wingers might worry about conspiracies to take away their guns, and left-wingers worry about their technological freedoms.”

We are all also affected by proportionality bias, which means that we assume big events have big causes. It doesn’t fit our intuition that an attack could be carried out by incompetent terrorists with a Lidl bag and fairy lights. Intentionality bias means we assume things happen because someone meant them to happen. “If there was a conspiracy to fake the bombing, then at least everything is under control," Brotherton says. "But if a handful of people can evade the authorities or slip through the cracks and cause chaos, that’s much more threatening.”

Emma now believes that the law needs to be changed so that others don’t experience the abuse she faced. “I was having threats, I was being called really vile names, and I couldn’t remove any of these comments,” she says. She contacted Twitter after someone created an image sharing all of her personal details, but says Twitter said it did not meet the criteria needed to take the tweet down. “[I’m] realising how much power Twitter and YouTube have over people's wellbeing,” she says, “and how extreme a circumstance you have to present to them for them to go ‘OK, we’re removing that person.' It really shocked me.”

Without help from Twitter, Emma took matters into her own hands. She Googled the man who left her a rape threat, found out where he worked, and contacted his employer. In many ways, she arguably used the tools of the trolls themselves – but it worked, with the man’s boss promising to look into the complaint. Perhaps more needs to be done to stop truthers spreading life-ruining lies, but this was a small victory for Emma.

“That’s the power of the internet,” she laughs.