The researcher, who identifies himself as Askai707, details evidence on his LiveJournal blog of alleged involvement one year ago of Russia's 6th Tank Brigade in a prominent strategic and symbolic battlefield win for the separatists.
Ukrainian forces suffered heavy casualties trying to capture the city of Ilovaysk in the Donetsk region in August 2014.
Pro-Russian forces had encircled them, and an agreement was reportedly reached by both sides to allow the Ukrainians to evacuate from inside what became known as the "Ilovaysk Kettle."
However, that deal was not honored and 366 Ukrainian soldiers, according to the Ukrainian military, were killed by pro-Russian forces while trying to escape in what many described as a massacre.
It was one of the Ukrainian military's most humiliating defeats in eastern Ukraine.
Kiev accused Moscow of sending in troops and tanks to help the rebels, and this fresh research appears to back Ukraine's claims.
Askai707 tracked down many of soldiers of Russia's 6th Tank Brigade, following their cybertrail thanks to their own social-media postings, namely on VKontakte, the biggest Russian-language social-networking site.
"I think it's very compelling. I think there's a good range of different sources that clearly point to Russian tanks and soldiers crossing in this specific incident," Elliot Higgins, the founder of Bellingcat, which has used open sources and social media to carry out its own widely acclaimed probe of Russian military involvement in the conflict in eastern Ukraine, including the downing of Flight MH17 over eastern Ukraine in July 2014, says of Askai707's findings.
'100 Percent Certain'
Bellingcat posted an English-language version of Askai707's post on its own site.
"Time and time again we're finding Russian equipment and Russian soldiers we can identify in Russia and then they head to the border and suddenly we see them in Ukraine,” Higgins told RFE/RL in a telephone interview on September 23.
He noted the similarity to Bellingcat's own research and said that "you find this time and time again with the Russian military."
"Loads of young guys who are serving, posting lots of pictures, and photographs, and reports online about their activities as part of the unit," Higgins said.
"It probably seems innocent when they're thinking, 'Oh, it's just one or two photos I'm posting,' but when you've got 200 guys in the same unit posting one or two photographs you've got a massive amount of information," Higgins said.
The report also tracks down a T-72B3 tank that was first captured by a Ukrainian unit and then seized back by the separatists.
"And what was interesting there was they pulled out a document from there that actually had the name of one of the soldiers [whom] the writer originally identified. When you've got those kind of documents being produced, as something separate from the actual investigation, I think that's very interesting indeed," Higgins said.
According to the website Military Today, the T-72B3 is an upgrade to the T-72B tank.
The first versions of this tank were reportedly delivered to the Russian Army in 2013.
Higgins said the Askai707 posting on September 17 had encouraged others to come forward on the Russian tank division in question.
"In fact, after this article was published on the tank unit, someone sent me a video that was published by a Ukrainian military unit, which actually showed what appears to be one of the soldiers from that unit who was captured inside Ukraine. Of course, at the time, it's very difficult to say, 'Well, are we sure these are Russian soldiers?' Because you don't have this body of evidence we now have," Higgins said.
"But now...we can be 100 percent certain, it's the same person in the video and the information that was collected, and yeah, he's definitely a Russian soldier because we have pictures of him serving in his unit and his tank."
Source: Radio Free Europe