The tea was laced with a radioactive isotope, polonium 210. Mr. Litvenenko fell ill that night at home and died of acute radiation syndrome Nov. 23 at University College Hospital in London.

Judge Robert Owen said Thursday in a lengthy report that he is certain Litvinenko was given tea laced with a fatal dose of polonium-210 at a London hotel in November 2006.

He was accused with ex-FSB operative Andrei Lugovoy, now a ultranationalist MP, of spiking Litvinenko’s tea with polonium-210 in a Mayfair hotel in London.