Friends and relatives follow the coffin of Sergei Magnitsky during his funeral at a cemetery in Moscow November 20, 2009. Human rights groups have called for an independent investigation into the sudden death of a 37-year-old witness in a Russian legal battle over tax fraud. Magnitsky, a suspect in a tax evasion case against Hermitage, once Russia's biggest investment fund, died of heart failure in prison on Monday, state prosecutors said. REUTERS/Mikhail Voskresensky (RUSSIA CRIME LAW POLITICS)