In the summer of 2012, a man was walking near Jabal Shashabo, a Syrian rebel enclave, when he spotted a group of turquoise canisters with what appeared to be tail fins attached. He picked up one of the objects and filmed it. Later he uploaded his video to YouTube.

What were those strange turquoise cans? The answer was provided not by a UN investigator, war correspondent or military expert, but by a bored business administrator at his desk in Leicester. He had never been to Syria, spoke no Arabic and by his own admission knew nothing about weaponry. But Eliot Higgins had become fascinated by the war in Syria, and was following the social media feeds of people in the thick of it. He saw the YouTube clip and noticed the serial number ‘A-IX-2’.

Working with other online amateur weapons-spotters, Higgins figured out that the man in the video was holding a Russian-made cluster bomb. These devices detonate at high altitude, sending out a shower of smaller bombs that often land without exploding. Children are especially likely to pick them up and be killed by cluster munitions, and for that reason they are illegal in many countries. By interrogating the contents of a single YouTube clip, Higgins had established that the Syrian government was using illegal, Russian-supplied cluster bombs against its own people. He published his findings online.

Then came the chemical weapons attack on Ghouta, the rebel-held suburb of Damascus, in which up to 1,700 people died. Higgins found images of the rocket on social media, and a detail caught his eye: the screw cap on the warhead suggested that it had contained liquid. After more online sleuthing, he concluded that the device was a Soviet-made artillery rocket and that the warhead had contained the nerve agent sarin.

This time Higgins went further. Using a combination of Google maps and extreme perseverance he was able to ‘geolocate’ the spot where the rocket had landed. From its angle of arrival, he deduced the rocket’s trajectory and therefore its launch site — a Syrian army installation. Higgins had shown that Assad’s army was using chemical weapons of Russian origin, in violation of international law. His investigations started attracting followers and he set up a blog, which he called ‘Brown Moses’.

It was the tragedy of flight MH17 from Amsterdam to Kuala Lumpur that brought his work to international attention. On 17 July 2014, during the Russian invasion of Ukraine, MH17 crossed into Ukrainian airspace. It was shot down, killing all on board. Using information that was openly available online, Higgins established that the plane had been hit by a Russian Buk missile. He also identified the serial number of the missile-launcher and even uncovered the identity of the shooters, in this case a unit of the Russian 53rd Brigade. In his report on the incident, he and his team concluded: ‘The Russian government bears responsibility for the tragedy.’

By this time Higgins’s blog had turned into an online research group, part-funded by Google, which he named Bellingcat. The name derives from the children’s story of the mice who decide to put a bell round the cat’s neck. By ‘belling the cat’, they take away its ability to act unseen.

Higgins and his team have been very effective at ‘belling the cat’. In 2018, they uncovered the identity of the men who poisoned Sergei and Yulia Skripal in Salisbury. In an absurd interview on Russian state TV, the two suspects claimed to have been tourists, visiting Salisbury to view the cathedral. Bellingcat established that they were GRU operatives, a kill team working for Russian military intelligence. Higgins’s work evidently touched a nerve. Sergey Lavrov, the Russian foreign minister, told an interviewer: ‘Bellingcat is closely connected with the intelligence services, which use it to channel information intended to influence public opinion.’

Higgins, whom I have met and interviewed, denies this. What’s more, he is completely unfazed by having made such powerful enemies. In a further investigation published after this book’s completion, Bellingcat identified the men who tried to assassinate Alexei Navalny, the Russian opposition leader. The culprits this time were operatives from the FSB, the Russian security service.

This determination to reveal awkward facts has led Bellingcat to focus on what Higgins calls ‘the counterfactual community’, the radical, conspiracy-obsessed online culture that has begun seeping out into the real world, with hideous consequences. As Higgins explains, the man who carried out the Pittsburg synagogue massacre in 2018 was radicalised by websites featuring anti-Semitic conspiracy theories, Nazi memes and ‘ironic’ white supremacist language. A mass murder at a Texas synagogue that same year was also announced on an extremist website, as was the 2019 Christchurch massacre at a New Zealand mosque.

The websites that radicalised these killers gave rise to conspiracy theories such as QAnon, popular among the Trump supporters who stormed the Capitol. QAnon’s followers believe that a cabal of child abusers, made up of senior Democrats and liberals, is trying to take over the world, and only Trump can defeat them. It’s absurd — but look at the social media images of the crowd that stormed Congress. Look at the QAnon flags and clothing emblazoned with the capital ‘Q’. A ridiculous theory, if widely believed, can threaten national security.

This is a fascinating, bewildering book. Remarkably, the world’s media failed to spot a gold mine of online information and it took a bored guy working in his spare time to show them the way. In doing so, he created an entirely new way of investigating events. Organisations including the BBC and the New York Times now have open source investigation units modelled on Bellingcat. In some cases, including the downing of MH17, Bellingcat’s findings have proved more revealing than investigations by governments and official bodies. Is its methodology more powerful than that of government agencies?

The distinction between the truth and the lie is often muddled, sometimes purposefully. Higgins worries that it will become even more blurred now that AI can generate ‘deepfake’ images of events that never happened. But the lesson of this deeply impressive book is that, despite the noise, the propaganda and the lies, the truth is everywhere. You just have to know how to look for it.