LONDON — Former Russian spy Alexander Litvinenko was poisoned by radiation, Britain's Health Protection Agency said Friday. Agency scientist Roger Cox said polonium-210 had been found in Litvinenko's urine. Earlier, Home Secretary John Reid said Litvinenko's death Thursday night was "linked to the presence of a radioactive substance in his body." Reid, the country's top law-and-order official, said experts were searching for "residual radioactive material" at a number of locations. The former KGB agent dictated a statement in the waning hours of his life, blaming Russian President Vladimir Putin and describing him "as barbaric and ruthless as your most hostile...