MOSCOW — Russian agent Dmitry Kovtun was acquitted by the U.K authorities of poisoning Alexander Litvinenko in London, in 2006. He died at the age of 57.

Andrei Lugovoi, a Russian lawmaker, was also accused by the U.K. of the spy’s murder. He announced Kovtun’s death via his messaging app channel. Lugovoi stated that Kovtun died on Saturday from a COVID-19-induced disease. Russian media reported that he died in a Moscow hospital.

British investigators concluded that Litvinenko had been killed by Kovtun, Lugovoi and that Vladimir Putin had “probably approved” of the operation. The British conclusion was supported by the European Court of Human Rights.

The Kremlin strongly denied any involvement.

Kovtun, Lugovoi and others denied any involvement in Litvinenko’s death.

Litvinenko, a former KGB agent and its post-Soviet predecessor agency FSB successor agency, defected to Russia in 2000 and fled for London. Litvinenko became involved in uncovering corruption and connections to organized crime within the Russian intelligence service.

After drinking tea with two Russian men at a London hotel, he became violently ill and died three weeks later. It was discovered that his tea had been laced radioactively polonium210.