MOSCOW ¨C Research collected by the slain anti-Kremlin leader Boris Nemtsov shows evidence that Russian troops fought and died in the conflict in Ukraine, fellow opposition activist Ilya Yashin said.

The report is being completed and will be published in April, Yashin said on Facebook on Monday. Friends of Nemtsov, who was shot dead near the Kremlin in February, have met sources representing relatives of those killed in Ukraine who had contacted the politician, he said.

¡°They were very afraid to speak when he was alive,¡± Yashin said. ¡°The death of Nemtsov, as you can understand, did not add to their bravery, so the contacts were achieved with difficulty.¡±

The murder of Nemtsov, a former deputy prime minister in the 1990s and an outspoken critic of President Vladimir Putin, shocked many Russians. Putin condemned the ¡°brazen¡± killing, while the liberal opposition accused the president of stirring up an atmosphere of hatred in which critics are branded fifth columnists on state television, amid patriotic fervor over the annexation of Crimea from Ukraine a year ago. The U.S. and the European Union accuse Russia of sending troops to support separatists in the conflict in eastern Ukraine, an allegation denied by the Kremlin.

Five men from Russia¡¯s mainly Muslim North Caucasus region were charged on March 8 in connection with the killing, after the Investigative Committee said it was examining the possibility that he was assassinated by Islamist extremists for his support of journalists killed at the French satirical magazine Charlie Hebdo in Paris.

Nemtsov¡¯s investigation into whether Russian troops are fighting in Ukraine showed evidence of two peak periods in which bodies of dead soldiers were transported back to the country, Yashin said.

The first occurred last summer, when about 150 bodies were returned to Russia during heavy fighting in Ukraine as rebel forces turned back a government offensive. The second ¡°wave¡± took place in January and February, when about 70 bodies were sent back during a period that coincided with the battle for the strategic town of Debaltseve in Ukraine.

Relatives of those who had died last summer each received about 3 million rubles ($52,000) in compensation, Yashin said. Relatives of those who were killed this year got nothing because the soldiers were required to resign formally from the army by their commanders before being sent to Ukraine.

¡°In this way, it was planned to hide the participation of our army in the military actions, presenting the soldiers as volunteers,¡± Yashin wrote. Soldiers were told by their senior officers that relatives would be compensated if they were killed, though no money was paid in practice, he said.