The two Russians had fled to the UK, and now both are dead. Nikolai Glushkov, who was once business partners with Boris Berezovsky, was found dead in his London home Monday night. Counterterrorism police are investigating the unexplained death "as a precaution because of associations that the man is believed to have had." The Telegraph calls Berezovsky, who opposed Putin and also died in unexplained circumstances in the UK in 2013, Putin's "arch enemy"; Glushkov and other friends insisted Putin ordered his murder. The paper calls Glushkov Berezovsky's "closest aide"; in the '90s he was a director at Berezovsky's car company as well as the state airline Aeroflot. Glushkov, variously reported as 68 or 69, left Russia for the UK, where he was ultimately granted political asylum, after Berezovsky fell out with Putin and left for the UK himself.
After Berezovsky's exit, Glushkov was charged with money laundering and fraud and spent five years in jail. He left for the UK out of fear he'd be arrested again; he denied all the charges against him. The Guardian has much more on that period of his life. Glushkov's death comes eight days after the poisoning of Russian double agent Sergei Skripal, but authorities say there is no evidence the two incidents are connected. In the Skripal case, Reuters reports Britain gave Russia a deadline of midnight Tuesday to explain how a Russian nerve agent was used against him, but Russia has pledged not to do so until samples of the nerve agent are handed over. President Trump Tuesday expressed support for Britain, saying if the US "agrees" with the facts, "we will condemn Russia or whoever it may be."