Moscow: The daughter of slain Russian opposition politician Boris Netmsov has filed a complaint over investigators' refusal to question Chechen leader Ramzan Kadyrov over her father's murder, her lawyer said on Wednesday.
Nemtsov, a 55-year-old former deputy prime minister who had become a vocal critic of President Vladimir Putin, was gunned down on a bridge just steps from the Kremlin in late February.
Five men suspected of carrying out the murder - including Zaur Dadayev, a former deputy commander in a special Chechen police unit - have been detained, but investigators have failed to identify the mastermind.
"We submitted a complaint today to Moscow's Basmanny district court about the Investigative Committee's refusal to interrogate not only Ramzan Kadyrov but also a string of other high-ranking Chechen officials," said lawyer Vadim Prokhorov, who represents Nemtsov's daughter, 31-year-old journalist Zhanna Nemtsova.
"It is time to remind the investigation that the organisers and those who ordered the murder have not been identified," Prokhorov told AFP.
Former allies of the murdered politician have pointed the finger at the Kremlin over the murder, while reports in Russia's opposition press have suggested ties between the killers and high-ranking Chechen officials.
Prokhorov claimed that Kadyrov had in the past threatened Nemtsov, and that the fact the Chechen strongman was acquainted with the murder suspects was enough to have him serve as a witness in the case.
"It is clear that those who were detained over the murder were not the ones who ordered it," he said.
Kadyrov has said he was baffled by Dadayev's arrest, who he claims was "one of the bravest and worthiest soldiers of his regiment".
He has suggested that Nemtsov's support for French satirical publication Charlie Hebdo over its caricatures of the Prophet Mohammed could have been the motive for the murder.
Islamist gunmen killed 12 people at the Paris office of Charlie Hebdo in January.
Kadyrov has enjoyed Putin's full backing as he has helped crush an insurgency in his home region with an iron fist.
Nemtsov's daughter has blamed official propaganda demonising Putin critics for her father's murder and wrote in a newspaper op-ed that "Russia's state TV channels, among others, bear responsibility".
Nemtsova announced in June she had left Russia indefinitely.