Boris Nemtsov, a charismatic former deputy prime minister turned Russian opposition leader, was shot and killed in Moscow Saturday, officials said. He was 55.
Nemtsov's death comes just a day before a planned protest against President Vladimir Putin's rule. The Kremlin said that Putin will personally oversee the investigation.
Nemtsov was a sharp critic of Putin, assailing the government's inefficiency, rampant corruption and the Kremlin's policy on Ukraine, which has strained Russia-West ties to a degree unseen since Cold War times.
The Russian Interior Ministry, which oversees Russia's police force, said that Nemtsov was shot four times from a passing car as he was walking a bridge just outside the Kremlin shortly after midnight.
Nemtsov served a deputy prime minister in the 1990s and once was seen as a possible successor to Boris Yeltsin, Russia's first elected president. After Putin was first elected in 2000, Nemtsov became one of the most vocal critics of his rule. He helped organize street protests and wrote extensively about official corruption.