A key Russian suspect in the 2006 killing in Britain of dissident former Russian agent Alexander Litvinenko has died after contracting COVID-19, a Russian lawmaker said Saturday.

“Sad news. My close and loyal friend Dmitry Kovtun has suddenly died following a grave illness linked to a coronavirus infection,” said Andrei Lugovoi, a member of the lower house of Russian parliament who was also accused in the case.

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“It is a terrible and irreparable loss,” he said in a statement.

The TASS news agency cited someone close to Kovtun as saying he had died in a Moscow hospital.

Europe’s top rights court in September ruled that Russia was responsible for the 2006 killing in London of Litvinenko, a verdict swiftly rejected by Moscow.

The Strasbourg-based European Court of Human Rights said there was a “strong prima facie” case that Lugovoi and Kovtun “had been acting on the direction or control of the Russian authorities.”

But in Moscow, Putin’s spokesman Dmitry Peskov rejected the claim.

Britain says Litvinenko died after drinking tea laced with the radioactive isotope Polonium 210 at a hotel, in a case that has weighed on relations between London and Moscow ever since.

British police identified Lugovoi and businessman Kovtun as prime suspects after they both met Litvinenko at a central London hotel.

But attempts to extradite them failed and they both rejected the charges, with Lugovoi also claiming parliamentary immunity.

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