Around 6:30 AM on Tuesday, April 4, 2017, before most children had left for school, Syrian Air Force Su-22 fighter jets launched missiles at the northern opposition-held town of Khan Shaykhun. Witnesses recalled a strange odor spreading after the missiles struck; people were choking and foaming at the mouth, and one resident later described how “they were suffocating while their lungs collapsed.” The airstrike contained a mixture of nerve agent–filled bombs and conventional munitions, according to James Le Mesurier, who founded the Syria Civil Defence (commonly known as the White Helmets). The White Helmets are Syrian first responders, and they are often the only rescue workers on the scene after airstrikes. Soon after the explosions in Khan Shaykhun, reports of a chemical strike were broadcast over local radio stations.

The casualties were taken to a nearby center run by the White Helmets, according to Le Mesurier. In this case, the White Helmets team didn’t know what type of agent had been used, so they began the standard protocol of washing down victims. While they did this, a number of the White Helmets were themselves exposed to the toxin (they survived). Victims were shuttled to medical centers in northern Idlib, and arrangements were made for them to receive medical attention in hospitals in Turkey.

Doctors in Turkey verified that some victims were suffering from symptoms of nerve-gas poisoning, including severe respiratory distress, vomiting, and intense stomach pain, said Le Mesurier. A few hours after the initial attack, conventional bombs hit a clinic where the wounded were being treated; by the end of the day, more than eighty people, many of them women and children, were dead. Hundreds had been injured.

In October 2017, the Joint Investigative Mechanism—a body created by the UN Security Council and the Organization for the Prohibition of Chemical Weapons to research chemical weapons attacks in Syria—confirmed that sarin had been used in Khan Shaykhun and that the Syrian government was responsible. The investigators drew heavily on the testimony of the White Helmets and on biomedical, soil, and clothing samples that were provided to them by the White Helmets, Le Mesurier confirmed. These samples were consistent with others gathered after the gassing, including those obtained by hospitals in Turkey.

Almost immediately after the attack, the Syrian regime initiated a disinformation campaign backed by its patron, the Russian government. Both had earlier claimed that a 2013 chemical attack in Eastern Ghouta, in which more than 1,400 people were killed, was perpetrated by the opposition—contrary to the conclusions of a UN investigation. They had also denied that atrocities such as the targeting of civilians and medical facilities were committed during the siege of Aleppo when regime jets bombed a US convoy. Aleppo fell to Syrian forces in December 2016. Now Syria and its Russian ally were set on denying what they called the “myth” that Khan Shaykhun had been gassed by government forces.

“The Syrian Army has not, did not, and will not use this kind of weapons,” Syria’s foreign minister, Walid al-Moallem, said in Damascus. In Moscow, Russian defense ministry spokesman Igor Konashenkov essentially blamed opposition fighters for gassing their own people. The Russian Ministry of Foreign Affairs began a propaganda campaign, largely relying on its agents and followers on Twitter to distribute falsehoods about the event. These included the claim that the chemical attacks were staged by the White Helmets using actors, as part of a Western conspiracy that was meant to provide cover both for the US airstrike on April 7 on the Shayrat air base and for a plot to bring down Assad by creating a pretext for military intervention.

The Russian and Syrian assessment of the attack was retweeted and hashtagged #SyriaHoax. According to the Syria Campaign, an international advocacy group that does not take money from governments, “Russia’s far-fetched claims were shared so widely, they became the number one trending topic on Twitter in the US.” A Syria Campaign study found that the Russian and Syrian propaganda reached many more people than did mainstream media coverage of the attack, which has also been the case at other points during the Syrian civil war; it also reported that “bots and trolls linked to Russia have reached an estimated 56 million people with tweets attacking Syria’s search and rescue organisation, the Syria Civil Defence—also known as the White Helmets—during ten key moments of 2016 and 2017,” including the Khan Shaykhun chemical attack, the nomination of the White Helmets for the Nobel Peace Prize in 2016 and 2017, the Aleppo offensive, and the 2016 murder of Jo Cox, a British member of Parliament who was a White Helmets supporter. It is a measure of the success of this disinformation effort that I am repeatedly asked by educated, well-informed people why Assad was accused of crimes that the opposition was carrying out. The de facto leader of the disinformation campaign is a blogger called Vanessa Beeley, who has been dubbed by The Guardian’s former Middle East editor as “the Syrian conflict’s goddess of propaganda.”

According to White Helmets’ founder Le Mesurier, the group, which first emerged in 2012 and now has about 3,000 members, has rescued some 115,000 people and lost more than 250 volunteers. One of the White Helmets’ most celebrated missions took place in 2014, when Khaled Omar Harrah, a former home decorator and father of two, pulled a ten-day-old baby out of the wreckage of a building after the infant had been buried for sixteen hours. (Harrah was killed in an airstrike in 2016.) A Netflix documentary about their work won the Academy Award in 2017, and Hollywood progressives have signed petitions in solidarity.

One strategy pro-Assad bloggers use to discredit the White Helmets is to argue that the group is funded by governments that, in the bloggers’ view, are intent on regime change in Syria. Part of the White Helmets’ funding comes from the British government’s Conflict, Stability and Security Fund, which oversees various global projects such as building dams in Central Asia and preventing sexual violence during war. Le Mesurier confirmed that the total UK government funding of the White Helmets had been about £38.5 million ($51 million) over a five-year period to March 2018. The US Agency for International Development (USAID) provided about $33 million over a similar period. The Qatari Red Cross has made a donation of about $1 million to the White Helmets, and other funding comes from the German, Canadian, Danish, and Japanese governments. These funds support the group’s budget of approximately $30 million a year, much of which is spent on equipment such as ambulances, fire trucks, and heavy diggers to recover bodies from collapsed buildings, and stipends for individual White Helmet volunteers, which are $150 a month.

But the White Helmets’ financial backing is not the real reason why the pro-Assad camp is so bent on defaming them. Since 2015, the year the Russians began fighting in Syria, the White Helmets have been filming attacks on opposition-held areas with GoPro cameras affixed to their helmets. Syria and Russia have claimed they were attacking only terrorists, yet the White Helmets have captured footage of dead and injured women and children under the rubble. According to Human Rights Watch and Amnesty International, as well as eyewitness accounts, Putin’s bombers have targeted civilians, schools, hospitals, and medical facilities in opposition-held areas, a clear violation of international law. “This, above all, is what the Russians hated,” Ben Nimmo, a fellow at the Atlantic Council specializing in Russian disinformation, told me. “That the White Helmets are filming war crimes.”

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Most of Assad’s Western apologists have a presence only on Twitter and obscure websites like 21st Century Wire (a website founded by a former editor of American conspiracy theorist Alex Jones’s Infowars), yet it would be foolish to disregard them. The work of this small group is also spread by a spectrum of far-left, anti-West conspiracy theorists; anti-Semites; supporters of Russia, Iran, and Hezbollah; libertarians; and far-right groups. At their core are Beeley, the daughter of a British diplomat; a Canadian activist named Eva Bartlett; the Hezbollah-friendly commentator Sharmine Narwani; and Max Blumenthal, the son of the former Clinton aide Sidney Blumenthal.

As The Guardian recently reported, the Russian government uses Twitter accounts belonging to its embassies, as well as other accounts that have been linked to the Internet Research Agency, which oversees trolls and bots, to spread disinformation. The views of pro-Assad writers also filter into the mainstream through more respectable Assad-friendly American and British journalists such as Robert Fisk, Stephen Kinzer, and John Pilger (who oversees the Martha Gellhorn Reporting Prize, which was previously awarded to Julian Assange, and for which Beeley was a runner-up). In turn, their reports are echoed by public figures such as the British MP Emily Thornberry, Baroness Cox, and the Reverend Andrew Ashdown, an Anglican minister.

The damage the bloggers do is immense. They attack anyone with an account of events that contradicts their own, but their chief target is the White Helmets. The bloggers’ work is repeated on the state-owned Russian news outlets RT and Sputnik; some of it has even been cited by Russian ambassadors at the United Nations. The bloggers resist being linked to the Kremlin, and there is no evidence of financial transactions other than the standard fees paid by RT for television appearances. But the Russian version of its own military strikes is amplified by bloggers like Beeley and Bartlett, who promote RT reports that push the Kremlin’s false narrative about the use of chemical weapons in Syria.

Beeley, a former consultant to a waste management company in the Middle East with no journalistic background, has only about 42,000 followers on Twitter, but she appears regularly on RT and Sputnik. Her posts are retweeted by the Ron Paul Institute, by members of the “alt-right,” and by what Muhammad Idrees Ahmad, a lecturer at the University of Stirling and an expert on the Russian disinformation campaign in Syria, calls “the Red–Brown alliance,” an unlikely coalition of far-left and far-right extremists.

Beeley first went to Syria in 2016 on a six-day trip to meet with Bashar al-Assad, an encounter she called “my proudest moment.” Shortly afterward, she flew to Moscow to meet with the Russian deputy foreign minister, Mikhail Bogdanov, who is Putin’s point man on Syria, and Maria Zakharova, Putin’s director of information and press. Following that visit, she began attacking the White Helmets vehemently. In 2015, she had called for the first responders to be killed, even though “violence to life and person [against civilians and non-combatants], in particular murder of all kinds” is prohibited by the Geneva Convention. “White Helmets are not getting it,” she tweeted. “We know they are terrorists. Makes them a legit target.”

Beeley has admitted, in a private Facebook conversation with the blogger Scott Gaulke that was obtained by hackers and subsequently published, that even Assad does not deny torture. She wrote, “even Govt members dont [sic] deny it btw,” adding that she would never admit this publicly. The reasons for her dedication to Assad’s regime, are, like those of other bloggers and writers like her, unclear. (Apparently, she sees Assad not as a war criminal, but as a victim of Western imperialism.) They may be “useful idiots” propped up by Russia, but their undying support of Assad is based on the anti-Western views that Syria was in line for US-led regime change, like Iraq. The fact that the Iraq invasion occurred under President George W. Bush, while President Obama resolutely refused to intervene in Syria—a stance that drew sharp criticism after the Assad regime first used chemical weapons—does not figure into their arguments.

Perhaps the most significant evidence of Beeley’s influence is that in May 2017 the deputy Russian ambassador to the United Nations, Petr Iliichev, submitted a paper titled “Information on the Work of the White Helmets in Syria” to the UN Security Council, trying to link the group to al-Qaeda. The document was based on a presentation Beeley had given earlier that year in London. In July 2017, Iliichev’s submission was rejected by eight countries on the Security Council, which affirmed its view that “Syria Civil Defense is an impartial, neutral group.”

Another pro-Assad blogger, the Canadian writer Eva Bartlett, spoke at the United Nations in December 2016, following a visit to Aleppo organized by the Assad regime after the fall of the city. Bartlett was introduced to witnesses who supported the Russian claims that the Assad alliance had been fighting Islamists, not bombing civilians. A video she made during her trip supported this narrative and was viewed at least 4 million times, which—for a writer not affiliated with an official news organization—is staggering. A version of it was promoted on the Russian state video site In the Now, with the caption: “Independent Canadian journo totally crushes MSM reporter on what’s actually going on in Syria.” Anna Nolan, the Syria Campaign’s former director, told me: “It was the most consumed piece of content around Aleppo, more so than any traditional media.”

Meanwhile, most mainstream journalists have been refused visas to visit regime-held areas of Syria. At the start of the war, I was initially allowed into regime territory but was followed by minders from the Ministry of Information. In 2012, after I went undercover and reported a government-sponsored mass killing in the town of Daraya, which was later verified by Human Rights Watch and “characterized by the UN appointed Independent International Commission of Inquiry as a ‘massacre,’” according to Amnesty International, my government visa was revoked and I was told I would be thrown in an “Assad prison” if I tried coming back. (Robert Fisk, who entered the town accompanied by government forces the day after I reported, denied any atrocities on their part, and continues to enjoy access to government-occupied Syria.) After Daraya, the only way for me—and most other mainstream reporters—to work was to cross into Syria via the Turkish border.

Another prominent pro-Assad figure is Max Blumenthal. In 2012, he resigned from his position as a reporter for the English-language website for the pro-Hezbollah Al-Akhbar newspaper in Beirut, for which he had written frequently about the plight of Palestinian refugees. In an open letter, he opposed to the paper’s pro-Assad views and its featuring of content by Sharmine Narwani and a writer named Amal Saad-Ghorayeb, whose work he called “malevolent propaganda.” In September 2013, Blumenthal went to Zaatari refugee camp in Jordan on assignment for The Nation. He strongly opposed US intervention against Assad, but he wrote on Twitter that “100% of dozens I spoke to in Zaatari today want US intervention in Syria.”

But then, in December 2015, as Russia was relentlessly bombing Syria, and doctors and civilians were being killed in Aleppo by barrel bombs, Blumenthal went to Moscow on a junket to celebrate RT’s tenth anniversary. We don’t know what happened during that visit, but afterward, Blumenthal’s views completely flipped. He has attacked not only the White Helmets but also Bana al-Abed, a nine-year-old girl who lived in rebel-held Aleppo and ran a Twitter account with her mother. The man who once wrote an essay called “The Right to Resist is Universal,” and attacked Narwani as an “Assad apologist,” now accuses anti-Assad Syrians of belonging to al-Qaeda and has claimed that the White Helmets were affiliated with the Islamist group.

The Australian reporter John Pilger echoes the views of Bartlett and Beeley in interviews. Pilger, who has a high profile in the UK because of his television documentaries criticizing US foreign policy, has a new platform on RT, which he uses to deny chemical weapons attacks such as the one at Khan Shaykhun. He, too, frequently attacks the White Helmets as Islamic extremists, and has cited Beeley’s writing as if it were authoritative journalism.

Unfortunately, the White Helmets have at times made mistakes that have been exploited by the group’s detractors. Under the organization’s charter, volunteers cannot carry arms, but several have been photographed with guns. (They were promptly fired.) Some volunteers have been photographed with black flags, which pro-Assad writers and social media users hold up as evidence of ties to jihadists, even though there are many groups in rebel-held Syria, not just al-Nusra or the Islamic State, that use black flags.

Perhaps most damaging was the participation of two members of the White Helmets in a viral video stunt called “The Mannequin Challenge,” in which people remain frozen like mannequins while someone films them. Without permission from supervisors, the two men posed in a staged shoot that made it seem as though they were next to an injured man; the Revolutionary Forces of Syria, the opposition media group that created the video, said its aim was to call attention to the situation in Syria. The video, filmed in November 2016, has been frequently cited by Assad supporters as proof that the White Helmets are a terrorist group, even though the video contains nothing about terrorism.

For those following events in Syria closely and witnessing Assad’s crimes, the spread of disinformation about chemical attacks is maddening. “So many self-declared progressives, who regularly point to war crimes committed by the US, Israel and the Saudi regime, deny or justify the torture, collective punishment and other atrocities committed by the Assad regime,” says Kristyan Benedict from Amnesty International, who regularly responds on Twitter to posts by Beeley, Bartlett, and others.

One measure of the regime’s enmity for the White Helmets is that Russian planes frequently launch secondary bombing raids known as “double tap” attacks in areas where they have earlier dropped bombs, in an attempt to kill members of the White Helmets as they try to rescue wounded Syrians—precisely the kind of attack that Beeley calls “legit.” “When we hear that noise, of the Russian planes coming back while we are on a site digging,” one White Helmets volunteer told me in 2015, “it is the most terrible sound in the world.” Another told me that being prevented from rescuing people suffocating under rubble “was worse than cruel, it was diabolical.”

The Assad regime and the Russians are trying to neutralize the White Helmets because they are potential witnesses to war crimes. But the White Helmets are far from the only source of such testimony. When the day for justice eventually comes, there will be enormous stores of evidence captured on smartphones by civilians and witnesses. The Syrian Archive in Berlin has collected and preserved over two million “digital units”—mostly recordings, but also photos, Facebook posts, and tweets—made by witnesses documenting potential human rights violations, though they estimate the potential number of evidential materials to be far larger than what has been gathered thus far. In a villa on the grounds of the United Nations’ Palais des Nations in Geneva, a group mandated by the UN General Assembly in 2016 and known as the International Impartial and Independent Mechanism (IIIM) is cataloging thousands of hours of documentation and reams of paperwork, some of which one day, we must hope, will be cited as evidence in war crimes charges.

The Russian mission from the UN has condemned the IIIM, calling it illegal, and refuses to recognize it. Most likely, Syria will not request an inquiry from the International Criminal Court. But the IIIM is supported by powerful European countries and is led by a French prosecutor who has a long record of bringing to justice war criminals from Cambodia and the former Yugoslavia. War criminals can be tried in other national jurisdictions, and the IIIM is already preparing cases against war crimes suspects from the Syrian conflict who are currently residing in France and Sweden.

UN Assistant Secretary General for Human Rights Andrew Gilmour has been following the Syrian situation closely since 2012. The Syrian government hasn’t allowed a single person from the Office of the United Nations High Commissioner for Human Rights to enter the country since 2014, Gilmour told me. “We operate on the pretty infallible assumption that any government which refuses to let us in has something big to hide from us,” he said.

For Syrians like Kassem Eid, who narrowly escaped the 2013 attack in Ghouta, the general denial of Assad’s attacks in Khan Shaykhun was excruciating. Checking his Twitter account in the days that followed, Eid was sickened by how quickly the pro-Assad camp was able to persuade ordinary people of its version. “I don’t know what’s more disgusting, committing genocide, or denying it and twisting facts,” Eid said. “As a survivor of Assad chemical weapons, I feel devastated every time he gasses more civilians. But I feel even more heartbroken when I see the propaganda denying it—or even accusing the victims of gassing themselves.”