Poisoning: British police request help from Moscow

British police investigating the poisoning death of a former KGB agent have officially requested assistance from their Russian counterparts, prosecutors said, as officers arrived in Moscow amid rising diplomatic tensions.

Meanwhile, lawyers for an imprisoned security officer, Mikhail Trepashkin, said he has key evidence in the case. They appealed to the British officers to collect testimony from him as soon as possible, saying his life is in danger.