The OSCE said shortcomings in Russia’s original investigation left many questions unanswered.
“His death was a tragedy for Russia and had a strong impact on the political climate, spreading fear and possibly opening up for further attacks and repression,” the OSCE said in a February 20 report.
Nemtsov was shot dead at close range on the Bolshoi Moskvoretsky Bridge, near the Kremlin in central Moscow, on February 27, 2015.
In June 2017, a Russian court sentenced a former Chechen battalion leader Zaur Dadayev to 20 years in prison for killing Nemtsov.
Four other Chechens were found guilty of involvement in the killing and sentenced to prison terms ranging from 11 to 19 years.
Critics, including relatives and colleagues of Nemtsov, say Russian authorities failed to determine who ordered the killing.
Some have expressed suspicions that the killing was ordered by someone within the inner circle of Russian President Vladimir Putin or Chechen leader Ramzan Kadyrov.
The OSCE report, prepared by the OSCE Parliamentary Assembly’s special rapporteur, Margareta Cederfelt, said “organizers and instigators” of Nemtsov’s killing must be held accountable to “instill hope among those in Russia who continue to risk persecution and attacks to fight for democracy and the rule of law.
“Despite calls both from within Russia and from other countries and from the international community to make sure Mr. Nemtsov’s murder was thoroughly, effectively, and transparently investigated so that both perpetrators, organizers, and initiators were held accountable, the official investigation and the following trial has been subject to severe criticism,” Cederfelt said.
Cederfelt cited “important work” by independent researchers and experts “in filling in the blanks” left by Russia’s official investigation.
“They have particularly pointed to the potential involvement of the Chechen leadership and/or security services, even suggesting that the Russian president may be the initiator,” Cederfelt said.
Cederfelt said that given the shortcomings of the official Russian probe, “such arguments can neither be dismissed nor confirmed.”
The killing of Nemtsov — a reformist politician, former deputy prime minister, and sharp critic of Putin — was condemned internationally.
Critics say Nemtsov’s killing has highlighted the dangers faced by Russians who oppose the Kremlin.
Supporters of Nemtsov, including members of the country’s opposition, plan to hold a mass rally in Moscow on February 29 to mark the fifth anniversary of his death.
Some opposition supporters also plan to use the rally to protest proposed amendments to the country’s constitution that critics say are aimed at extending Putin’s grip on power after his current presidential term ends in 2024.