MOSCOW (AP) — Thousands of people streamed to a Moscow bridge overlooking the Kremlin on Saturday to lay flowers and mark the sixth anniversary of the killing of Boris Nemtsov, a top Russian opposition figure.

Nemtsov, 55, a former deputy prime minister, was shot to death as he walked along the Bolshoi Moskvoretsky bridge late at night on Feb. 27, 2015.

Among those who attended Saturday's commemoration was Yulia Navalnaya, the wife of imprisoned Russian opposition leader Alexei Navalny.

Navalny's detention in January upon returning to Moscow from five months of recuperating in Germany from a nerve-agent poisoning set off a wave of nationwide protests.

Nemtsov was one of Russia’s most energetic and charismatic opposition figures, and his death was a blow to political opponents of President Vladimir Putin.

An officer in the security forces of Chechnya’s Kremlin-backed leader was sentenced to 20 years for firing the shots that killed Nemtsov. Four other men were sentenced to 11 to 19 years for involvement.