Sergei Skripal was poisoned by agents of the same shadowy but buccaneering Russian intelligence agency he served in and betrayed decades ago, British authorities claimed.
Alexander Petrov and Ruslan Boshirov, named as suspects in his attempted murder and of his daughter Yulia in Salisbury, are agents of the GRU, the Russian Ministry of Defence's elite intelligence and special forces arm, British Prime Minister Theresa May told the House of Commons.
There is barely any information available about the pair, they are almost certainly commissioned Russian military officers highly trained in covert operations, espionage and assassination.
After releasing photographs of the two well-built men in their 40s, police said they were travelling under aliases.
Fontanka, an independent Russian news agency, reported that the men's passports were issued in 2016 and that they travelled to Amsterdam, Geneva, Milan and went several times to Paris before their trip to Salisbury, but offered no confirmation for the claim.
On paper, the GRU, or Main Intelligence Directorate, combines two roles — an intelligence branch, roughly the equivalent of Britain's Defence Intelligence department, and the Spetsnaz brigades, the Russian version of the SAS and SBS.
But unlike the FSB and SVR, the domestic and overseas spy agencies that emerged from the break-up of the KGB, it has never been a civilian outfit.
And its bat-and-globe emblem embodies a military ethos that has put it at the spearhead of the Kremlin's boldest and bloodiest covert operations of recent years.
"The GRU essentially thinks of itself as a war-fighting agency, and it combines covert intelligence work with special forces mindsets," said Mark Galleotti, an expert on Russian intelligence agencies. "That makes it more of a risk-taking organisation than its counterparts — it is more important for them to take a chance than worry about the risks."
Recruitment to the agency is strictly via the armed forces, and those who get in are part of a hand-picked elite.
"It is impossible to volunteer for the GRU, you can only be invited," said Boris Volodarsky, a long-serving former GRU officer. The usual career route sees a promising commissioned officer recommended for selection by a superior.
The candidate then goes before a vetting commission, and if approved is enrolled in the Frunze Military Academy in Moscow, where he will spend up to four years studying tradecraft before being joining the agency's intelligence arm.
They might then go on to serve as military attaches in foreign embassies, recruit spies to glean information from other countries' military plans, or plan complex special operations.
Skripal was recruited into the agency after serving as a Soviet paratrooper officer and was posted to the military attaches' officers at embassies in Malta and Spain.
But he betrayed the agency when he was recruited to be a British double agent — handing MI6 the names of dozens of key agents.
There is a slightly different career path for the Spetsnaz, which also come under the GRU umbrella. Their work is elite war-fighting and soldiers go through gruelling training regimes. They have been deeply involved in Russia's campaigns in Syria and Ukraine.
It is not clear which branch Petrov and Boshirov served in. Volodarsky said the GRU intelligence branch would be in charge of a delicate, non-battlefield assassination against a target like Skripal.
HOW THEY DID IT
• The two senior GRU officers dispatched to carry out the attack were named as Alexander Petrov and Ruslan Boshirov. The men, in their 40s, flew to Britain under false identities, using passports issued by the Russian state.
• CCTV images showed the officers in Salisbury minutes before Colonel Sergei Skripal, 66, and his daughter Yulia, 33, were poisoned with Novichok smeared on their front door handle.
• They touched down at Gatwick on Friday, March 2, using a £49-a-night east London hotel as their base. Traces of the weapons-grade nerve agent were found in the hotel room.
• The Novichok was smuggled in a fake Nina Ricci perfume bottle with an adapted nozzle.
• The men went to Salisbury for reconnaissance, returning again the following day. That was when it is believed they contaminated the front door.
• On March 4, the pair boarded an Aeroflot plane at Heathrow airport and returned to Moscow.
• The bottle was discarded in a bin by the hitmen and picked up by Charlie Rowley, 45, who gave it to his girlfriend Dawn Sturgess, 44. She died after applying the nerve agent to her wrists.
— Telegraph Group Ltd, Washington Post