Allies of murdered Russian opposition leader Boris Nemtsov on Tuesday unveiled a report based on research he collected that they claimed proved Russian military involvement in Ukraine. The 65-page report called "Putin and War" said the Russian army made two major incursions into Ukrainian territory in the summer of 2014 and in the winter of 2015. The first deployment of the regular Russian army to eastern Ukraine resulted in the deaths of soldiers, with "more than 150 coffins" returning to Russia, while in the winter "at least 70 troops died," said Ilya Yashin, one of the authors of the report. The Kremlin refused to comment on the claims.

A Russian military presence in Ukraine was verified on February by the United States State Department saying that "Russian units along the border with Ukraine are preparing a large shipment of supplies to pro-Russian forces fighting in eastern Ukraine." Putin rejected the charges that Moscow has backed, armed and financed the pro-Russian separatist groups in the embattled east of the country, calling the conflict-torn region a part of Russian territory.

Following the killing of the prominent Russian opposition leader, Boris Nemtsov, Russia has become a hive of rumor with people having a variety of interpretations over the murder. Relating findings of the assassination to Russia's assertive policies in the Ukraine crisis, the Ukrainian President Petro Poroshenko blamed the Kremlin for Nemtsov's death, claiming that Nemtsov was preparing to publicly share a report at Sunday's opposition rally that disturbed Russian authorities. "Somebody was afraid of this, Boris wasn't afraid. Killers and executors were afraid," the Ukrainian president said, referring to the report Nemtsov had been working on, detailing the presence of Russian troops in Ukraine, a claim the Kremlin strictly denies.

The murdered Russian opposition politician was widely known for his tough stance against Russian President Vladimir Putin's rule. He was also a powerful critic of not only the Moscow government under Putin's rule but also Russian foreign policy over Ukraine since the tension flared up in Ukraine in 2004 with the Orange Revolution.