The four Russians arriving at Amsterdam’s Schiphol airport looked like classic business travellers. Two of them – Alexey Minin and Oleg Sotnikov – strolled casually through arrivals. Sotnikov, head down, looked as if he was making a joke. Just behind were a pair of younger men, both going bald. They were Evgenii Serebriakov and Alexsei Morenets.

The travellers were thirty- and fortysomething Russian diplomats. At least, that is what their passports said. Clearly they were on a mission of some kind; a tie-wearing official from Russia’s embassy in the Netherlands came to the airport to greet them. But the precise reason for their trip from Moscow to Holland was unknown.

In fact the group were not tourists, as they would later meekly claim. They were undercover officers working for the GRU – the Main Intelligence Directorate of the General Staff of the Armed Forces of the Russian Federation. Of Russia’s three spy agencies, the GRU is the biggest and the most powerful.

The four intelligence officers who arrived in Holland belonged to a covert GRU cyberhacking team, investigators believe. Their trip to the country was merely the latest in a series of secret international assignments. Their target this time was the Organisation for the Prohibition of Chemical Weapons (OPCW).

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The circular HQ of the OPCW was in The Hague, downtown, an hour’s drive away. The four men hired an inconspicuous black Citroën C3 car and set off. It was Tuesday 10 April 2018. Each man had a defined role. Morenets and Serebriakov were cyber-operators. Minin and Sotnikov were responsible for reconnaissance and were there to make sure nothing went wrong.

It was not difficult to guess why Moscow might want to hack OPCW communications. The previous month two GRU officers had tried to kill a former colleague, Sergei Skripal, in Salisbury. They used the nerve poison novichok. The plot had not worked – Skripal was alive – and the UK government had publicly accused the Russian state of attempted murder.

The Kremlin vehemently denied this. The OPCW was about to release the results of its investigation into the Skripal case , findings that would confirm Downing Street’s claims and lead to international condemnation. Meanwhile, in Syria, another chemical weapons attack had taken place in the city of Douma. The west blamed the Assad regime; Moscow the rebels.

The next day Minin scoped out the target, according to Dutch investigators. He took photos of the OPCW building and the Marriott hotel next door. He went back at least twice. The operation was slated for Friday 13 April. The Russians drove their vehicle to the Marriott, and parked just across the road from the OPCW, under a dull spring sky.

GRU operatives are meant to be part of an elite spy cadre – highly trained professionals, dedicated to the motherland, and schooled in operational warfare. In reality the four turned out to be bungling amateurs. Seemingly, British intelligence knew of the plot in advance. They tipped off their Dutch colleagues. The men were closely tracked.

When the Dutch swooped they discovered sophisticated equipment hidden in the car’s boot: a computer, a 4G smartphone, a transformer and battery bag. There was also a white rectangular wifi panel antennae covered with a dark coat. The spies bought the battery in The Hague and kept the receipt. Serebriakov had brought additional devices for hacking wifi connections.

Facebook Twitter Pinterest The boot of a vehicle found outside the Organisation for the Prohibition of Chemical Weapons, in The Hague. Photograph: Dutch Ministry of Defence

There were further tell-tale clues. The GRU officers took their rubbish with them from their hotel rooms: tins of green Heineken and empty fruit juice bottles, found in the vehicle in a plastic shopping bag. They had a lot of cash for breezy sightseers from Moscow: $20,000 and €20,000, sorted into crisp hundred-dollar bills.

The most spectacular evidence was retrieved from seized cellphones and a camera. One of the men tried to destroy his mobile, further proof, according to the Dutch, that the group had received security training. One phone had been switched on for the first time, on 9 April. The location, identified by a cell-tower, was the GRU’s barracks in Moscow’s Komsomolsky Prospekt.

Unlike James Bond, officers engaged in real-life international espionage need to account for their expenditure. And so Morenets snapped a copy of his taxi receipt. It revealed that on 10 April he went by taxi from the GRU’s HQ in Nezvishkiy Pereulok to terminal F of Sheremetyevo airport. His 32km journey cost 842 roubles (£10). We do not know if he was repaid, or if he left a tip.

The firm Be Taxis confirmed the receipt was real. “Yes, this is ours. The driver Tsvetkov is now on a shift,” a company employee said.

By late spring, western intelligence agencies had pieced together a comprehensive picture of the GRU’s cyber operations abroad. Its sweep was astonishing. At a time when Moscow was accused of running a state-sponsored doping programme, Serebriakov had travelled in August 2016 to the Olympic games in Brazil. Found on his laptop was a photograph – the spy with an unknown young woman wearing a “Russia” T-shirt.

In December 2017 Serebriakov flew to Malaysia’s capital, Kuala Lumpur. He stayed at the Grand Millennium hotel. Dutch prosecutors say he was targeting Malaysia’s chief prosecutor and police. They were investigating MH17, the Malaysian airliner shot down in the summer of 2014 in eastern Ukraine by a Buk anti-aircraft missile. The launcher came from Russia, Dutch investigators believe.

Days later Serebriakov was using a wifi hotspot in Lausanne, Switzerland. He appears to have checked into the Alpha-Palmiers and Palace hotels. His apparent goal was to hack into the World Anti-Doping Agency (Wada) and to infect its systems with custom-built GRU malware.

Facebook Twitter Pinterest The four men pictured at Schiphol airport. Photograph: Dutch Ministry of Defence

At the time Wada was briefing the International Olympic Committee on its long-running investigation into Kremlin doping. Wada had long been a Moscow target: one recovered laptop was registered to a hotel network in 2016 where the Wada congress was being held.

The Hague was not the final stop of the GRU team’s mini-tour. The group bought a train ticket for 17 April from Utrecht to Bern, Switzerland. The ostensible target this time was the Spietz laboratory, near Bern, which had been testing samples provided by Britain. The lab confirmed the substance used against Sergei Skripal and his daughter, Yulia, was novichok.

The Russians caught in Holland were not diplomats; rather, they were veteran members of the GRU’s Sandworm cyber unit. Their mission could hardly be deemed a success. They were expelled.

The Kremlin’s denials may work inside Russia but will convince few in western countries, where governments are increasingly weary of hyper-aggressive Russian operations.

After Thursday’s revelations no one can be in any doubt of the GRU’s staggering ambition and global footprint. It has been a bad spell for the agency, which has suffered setbacks in Salisbury and The Hague. It may spend a little time updating tradecraft and its expenses policy. But its officers will carry on and continue to probe for weakness in “enemy” defences.