Glushkov's death was a eerie echo of his friend Boris Berezovsky, an exiled Russian oligarch and an outspoken critic of Putin who was found in 2013 with a rope around his neck — and whose death was initially a suspected suicide. It was reclassified as unexplained.
"Boris was strangled," Glushkov said afterward in an interview with The Guardian newspaper. "Either he did it himself or with the help of someone. [But] I don't believe it was suicide."
So far, police said, there is no link between the death of Glushkov and "the attempted murders in Salisbury, nor any evidence that he was poisoned.”
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That was a reference to the attempted assassinations of former Russian double agent Sergei Skripal and his daughter Yulia, who were found unconscious last weekend on a bench in the city of Salisbury — and who police later said were poisoned with a nerve agent.
They remain in crucial condition and British Prime Minister Theresa May has said it was “highly likely” they were the victims of an attempted hit by Russian military intelligence.
The Russian ambassador in London insisted the British were keeping diplomats in the dark about Glushkov’s murder.
"The embassy has no information about the launch of the probe into Glushkov’s murder,” Alexander Yakovenko said. “The British side is not responding to the embassy’s inquiry. It is unacceptable and we consider this situation as a failure of the U.K.’s international liabilities under the Vienna convention of consular access."
Glushkov also once testified in court against the billionaire Roman Abramovich, a Putin ally who owns the Chelsea Football Club, an English soccer team.
Berezovsky was a close friend of former Russian spy Alexander Litvinenko, who died from radioactive poisoning in 2006. An inquiry by British investigators concluded that his death was the work of the Russian state and was probably green-lighted by Putin himself.
On Friday, British Foreign Secretary Boris Johnson said Britain's quarrel was not with the Russian people but with the Kremlin.
"Our quarrel is with Putin’s Kremlin, and with his decision – and we think it overwhelmingly likely that it was his decision — to direct the use of a nerve agent on the streets of the UK."
Kremlin spokesman Dmitry Peskov called the allegation that Putin was involved "a shocking and unforgivable breach of the diplomatic rules of decent behavior," TASS news agency reported.
Citing U.S. intelligence sources, BuzzFeed reported that the deceased were suspected of being assassinated on British soil by Russian security services or mafia groups, "two forces that sometimes work in tandem."