This conclusion was made and announced by Bellingcat. It was made on the basis of the fact that the Buk system was accompanied by a convoy that was composed of 1 gray Rav4 SUV, a camouflaged UAZ, and a dark blue Hyundai van with tinted windows. The RAV4 is seen in a photograph shared by the tabloid Paris Match.
Besides, a UAZ-469 jeep was seen with the Buk in Torez just after noon, likely a couple of hours after it had left Donetsk.
Both photos were taken on July 15, two days prior to the catastrophe. The two vehicles that strongly resemble the vehicles photographed near the Buk and mentioned in the early morning VK post were described, photographed, and filmed in a separatist convoy headed to Donetsk two days before the downing of MH17.
Therefore, the Buk missile launcher seen in eastern Ukraine was under Russian/separatist control.
As previously reported, Bellingcat criticizes calculations presented by Russian manufacturer of Buk which supposedly was used to down MH17.