Mourning Nemtsov 

People hold flags and posters during a march to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, near St. Basil's Cathedral in central Moscow, March 1, 2015. REUTERS/Sergei Karpukhin

A couple embraces during a march to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in Moscow, March 1, 2015. REUTERS/Maxim Shemetov

People march behind a banner to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in central Moscow, March 1, 2015. REUTERS/Maxim Zmeyev

People hold placards and Russian national flags during a march to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in central Moscow, March 1, 2015. REUTERS/Maxim Shemetov

A poster of Kremlin critic Boris Nemtsov, who was shot dead on Friday night, is seen during a march to commemorate him near St. Basil's Cathedral in central Moscow, March 1, 2015. REUTERS/Sergei Karpukhin

People attend a march to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in central St. Petersburg, March 1, 2015. REUTERS/Peter Kovalev

A man waves Russian national flag during a march to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in central Moscow, March 1, 2015. REUTERS/Maxim Zmeyev

People lay down flowers at the site, where Kremlin critic Boris Nemtsov was murdered on Friday night, during a march to commemorate him in central Moscow, March 1, 2015. REUTERS/Tatyana Makeyeva

People hold posters during a march to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in central Moscow, March 1, 2015. REUTERS/Sergei Karpukhin

A woman holds a candle as she attends a march to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in central Moscow, March 1, 2015. The signs read, "No words". REUTERS/Maxim Shemetov

People hold placards to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in central Moscow, March 1, 2015. REUTERS/Sergei Karpukhin

Petr Tsarkov, co-chairmen of the Solidarnost ("Solidarity") opposition movement, holds a poster of Kremlin critic Boris Nemtsov during a march to commemorate him in central Moscow March 1, 2015. REUTERS/Sergei Karpukhin

People carry Russian national flags as they walk in a march to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in Moscow, March 1, 2015. REUTERS/Maxim Shemetov

People march behind a banner to commemorate Kremlin critic Boris Nemtsov, who was shot dead on Friday night, in central Moscow, March 1, 2015. REUTERS/Maxim Zmeyev

A man holds a poster of Kremlin critic Boris Nemtsov, who was shot dead on Friday night, during a march to commemorate him in central Moscow, March 1, 2015. The sign reads, "He died for the future of Russia". REUTERS/Sergei Karpukhin