MOSCOW: A second Russian witness in the investigation into the radiation murder of the former security agent Alexander Litvinenko has fallen ill from a similar radiation poisoning, medical sources said. Russian businessman Andrei Lugovoi had been subject to "radioactive exposure in dangerous doses," the sources said. Mr. Lugovoi's business partner Dmitry Kovtun, another key witness in the Litvinenko case, is reported to be in "critical condition." Mr. Lugovoi and Mr. Kovtun, who are now in hospital in Moscow, met Litvinenko at London's Millennium Hotel on November 1, the day Litvinenko fell ill. He died three weeks later from poisoning by polonium-210.