MOSCOW, July 9 — The American ambassador to Russia, William J. Burns, urged the Kremlin on Monday to “redouble its efforts” to solve the case of the American journalist Paul Klebnikov, who was shot three years ago in a contract murder here. The ambassador spoke at a gathering of Mr. Klebnikov’s family and friends here at the Cathedral of Christ the Savior. Mr. Klebnikov, an American of Russian...