Personal data: Bair Guroyev (archive), hails from the village of Ust-Obor, the Petrovsk-Zabaykalsky distict, Zabaykalsky Krai of the Russian Federation. (Profile, album, contacts, car number (X581XX  archives).
Judging by the photos, Guroyev was enlisted after conscription in 2012 (archive 1, archive 2).
Specific chevrons, equipment, soldiers' ethnicity, inscription "Ulan-Ude," and other evidence of military service in 2013 testify it was the Tatsinskaya-based 5th Separate Armored Brigade, military unit No. 46108.
Then, there was a small period of civilian life after which, in the second half of 2014, a new series of photographs evidencing of contract service in the same military unit followed (archive 1, archive 2).
The period from December 2014 to February 2015, when the soldiers were taken out for exercises, proved to be rather eventful. During this period, Guroyev posted photos with a moving column of military hardware bearing a well recognized flag of the so-called "DPR" (archive).
The photo is dated Feb. 25 2014; it was shot by Guroiev himself, sitting on his tank. It was possible to identify the area by the picture - the Shyrokyi district of the Ukrainian Donetsk, Lenina Avenue. The exact place of the image was found with the help of Google Street View.
The photo shows the well-known tactical sign of militants - white square loop. Equipment with such marking was repeatedly recorded in the anti-terrorist operation (ATO) area in Ukraine.
In some February photos, Russian soldiers wear the uniform without insignia:
After completion of the "exercises" in the Donbas, war criminal Guroyev continued to serve in the 5th Separate Armored Brigade, at least until the end of summer 2015 (archive 1, archive 2). In the photo of Aug. 30, 2015, Bair is wearing the chevron of military unit No. 46108 (archive). This fact confirms the hypothesis of his serving as a contract soldier throughout the entire stay in the Donbas.