LONDON — A prominent Russian dissident was assassinated in London with a deadly dose of radioactive poison because he had claimed that Vladimir Putin was a pedophile, according to an independent British inquiry.

The hit was “probably” carried out on the personal orders of the Russian president.

The allegation—that Putin had used his position as head of the Russian intelligence service to destroy video evidence of himself having sex with underage boys—was “the climax” of an increasingly bitter personal feud between Alexander Litvinenko and the Kremlin leader.

Sir Robert Owen, a retired High Court judge, found that this personal animosity, combined with Litvinenko’s continued criticism of the Kremlin and the FSB, of which he was once a senior member, was the motive behind his brazen murder in a Mayfair hotel via a pot of green tea laced with the radioactive isotope polonium-210 in November 2006.“The FSB operation to kill Mr. Litvinenko was probably approved by Mr. Patrrushev, then head of the FSB, and also by President Putin,” Owen told the Royal Courts of Justice on Thursday.

“There was undoubtedly a personal dimension to the antagonism between Mr. Litvinenko on the one hand and President Putin on the other,” he wrote in his report. “Mr. Litvinenko made repeated highly personal attacks on President Putin culminating in the allegation of pedophillia in July 2006.”

The claim was made in an article on the Chechen separatist website Chechenpress shortly after Putin was filmed lifting the T-shirt and kissing the stomach of a young boy at the Kremlin.

Litvinenko claimed this display of affection was the first public sign of a secret that had long been known by some within the KGB. He said Putin had been denied a place in the foreign intelligence division as a young recruit “because, shortly before his graduation, his bosses learned that Putin was a pedophile.”

“Many years later, when Putin became the FSB director and was preparing for the presidency, he began to seek and destroy any compromising materials,” Litvinenko wrote. “Among other things, Putin found videotapes in the FSB Internal Security directorate, which showed him making sex with some underage boys.”

Thursday’s announcement has been 10 years in the making. The British government rebuffed Marina Litvinenko’s pleas for an inquiry into her husband’s assassination for eight years because diplomats feared that London’s improving relationship with Moscow would be severely damaged.

A secret letter written to Owen by the Home Secretary Theresa May in 2013 explained why no inquest had been allowed. “It is true that international relations have been a factor in the government’s decision-making,” she admitted.The government would change its mind a year later, when Russia’s conflict with Ukraine and the shooting down of passenger jet MH17 ended diplomatic niceties.The explosive conclusion of the report will do little to calm relations between the nations, even though Owen stops short of saying he has conclusive proof that Putin ordered the hit directly.

The inquiry heard that two Russians, Andrei Lugovoy and Dmitry Kovtun, carried out the killing a few yards from the U.S. embassy in London by pouring polonium-210 into a pot of tea they offered to the former Russian spy.

Neither man still worked for the Russian state directly—Lugovoy had left the FSB and Kovtun was no longer employed by the Army. But Owen quoted an old Russian saying in his 300-page report: “There is no such thing as a former KGB man.”

On day 22 of the inquiry, when ample evidence had already been heard that Lugovoy was behind the killing, President Putin gave him a national award “for services to the fatherland.”

Owen wrote: “Mr. Lugovoy’s award, given in particular its timing and public nature, can only be interpreted as a deliberate sign of public support made by President Putin... It can be inferred from these facts that the Russian State approves of Mr. Litvinenko’s killing.”

On Thursday, Marina Litvinenko spoke on the steps of the court to welcome the verdict. “I am of course very pleased that the words my husband spoke on his deathbed when he accused Mr. Putin have been proved by an English court.”

But she was less complimentary about the British government, which has been briefing journalists that it will not levy severe sanctions against Moscow at such a sensitive time in negotiations over the future of Syria, ISIS, and President Bashar al-Assad.

The widow wants a British version of the Magnitsky Act, which President Obama signed in 2012 imposing sanctions against the killers of Sergei Magnitsky.

“I’m also calling for the imposing of targeted economic sanctions and travel bans against named individuals... including Mr. Putin,” she said. “It is unthinkable that the prime minister would do nothing in the face of the damning findings of Sir Robert Owen.”

The British government announced Thursday that it would freeze the assets of Lugovoy and Kovtun and issue international arrest warrants, even though Russia has made it clear the men will not be extradited.

For a litany of reasons, Alexander Litvinenko was not a popular man in Moscow. As he lay in ward T16 at University College Hospital on Nov. 18, 2006, two Scotland Yard detectives on the graveyard shift were about to discover why.The pale patient, who was experiencing excruciating but unexplained pains, had been booked into the hospital as Edwin Redwald Carter. After two weeks at a smaller hospital in North London, he had been moved to the city’s top medical facility by doctors who could not work out what had made him so sick.His symptoms were consistent with radiation poisoning, but Geiger counters showed no sign of radiation. As his condition worsened, thalium was another suspected cause, but no trace was found.Clueless as to what substance was gradually destroying his body from the inside, “Edwin Carter” and his wife were increasingly convinced that he had been poisoned. They called in the police.Detective Inspector Brent Hyatt and Detective Sergeant Chris Hoar arrived at around midnight to ask why they thought poison had been used. They were stunned by what they were about to hear.

“In Russian, I have [another] name: Alexander Litvinenko,” Carter began, in faltering English. “I am former KGB, FSB officer.“1997, I sent to top secret department of KGB my, my department has duty killing... political and high business men without verdict—judge verdict.”He said the first target of these extrajudicial killings was to be Boris Berezovsky—a fallen ally of Putin.“After I, I had this order, I said to my boss, ‘I’m, I refuse take this.... It’s not right, is not justice.’”

And so began Litvinenko’s post-FSB career, which included a series of lurid claims about Russia’s mafia state. Once he had escaped Russia and was granted political asylum in Britain in 2001, he claimed the KGB and the FSB had been run through with corruption, accused it of murders, kidnappings, and drug-dealing and, most extraordinarily of all, staging a false-flag terror operation in Moscow.He alleged that the 1999 Moscow apartment bombings, which killed some 300 people, were masterminded by Russian security forces in order to justify a full-scale war against Chechnya and bolster the popularity of a young, hardline prime minister named Vladimir Putin.Litvinenko was paid $2,800 a month as an informant for MI6—Britain’s foreign intelligence service. He also took a salary from Berezovsky, the man he says he was once ordered to murder. The oligarch had also fled Russia and was granted asylum in the U.K. in 2003.Berezovsky, who was found hanged in March 2013, paid Litvinenko to help him research and write articles and publications that were critical of Putin. Litvinenko also offered himself for hire to private intelligence companies, and the inquiry heard that he had been working for the Spanish authorities, who were trying to crack down on Russian crime syndicates operating there.In the spring of 2006, Litvinenko met the famous activist journalist Anna Politkovskaya in a coffee shop in London. He asked her to leave Russia and continue to fight against Putin’s regime from outside the country.She decided to stay in Moscow and was shot dead in the elevator inside her apartment block on Oct. 7. In the following weeks, Litvinenko told a gathering at the Frontline Club, a foreign correspondents’ association in London, that Putin had ordered her assassination.A month later, he was gravely ill and recounting his own extraordinary tale to a pair of confused Scotland Yard detectives.

The inquiry heard several theories about who had ordered two former Russian agents to strike him down in what was described as “a nuclear attack on the streets” of London. In one theory, he was silenced before he could publicly describe links between Spanish criminal networks and senior Russian officials.

The inquiry also heard that Litvinenko had written a report that claimed that Viktor Ivanov, the head of Russia’s narcotics agency, had links to the Russian mafia and was engaged in drug trafficking and money laundering while working closely with Putin in St. Petersburg in the 1990s.

Litvinenko himself seemed relatively unconcerned about which one of his public statements had ultimately cost him his life.

He told the detectives at his bedside: “I have no doubt whatsoever that this was done by the Russian Secret Services. Having knowledge of the system, I know that the order about such a killing of a citizen of another country on its territory, especially if it is something to do with Great Britain, could have been given by only one person.”

Detective Inspector Hyatt: “Would you like to tell us who that person is, sir?”

“That person is the president of the Russian Federation: Vladimir Putin,” Litvinenko replied.

Thanks to a radioactive breadcrumb trail that led all the way back to Moscow, the manner in which he was murdered also became obvious in the end.

As Litvinenko’s condition deteriorated, doctors decided to send a sample of his urine to the U.K. Atomic Weapons Establishment to see if they could detect any radioactivity. There, scientists discovered massive alpha radiation—the substance emitted by polonium-210, which would have been undetectable by medical staff, pathologists, or law enforcement.

Once the nuclear scientists had discovered its presence, it was easy to retrace the steps of Lugovoy and Kovtun.