There is one important reason Ukrainian authorities are so sure that pro-Russian rebels shot down a Malaysia Airlines jet: An account on the Russian social network Vkontakte, which relays official dispatches from insurgent military leader Igor Girkin, aka Strelkov, boasted about the rebels shooting down a plane at about the time of the crash.

The Boeing 777, on its way from Amsterdam to Kuala Lumpur with 295 people on board, crashed between the village of Grabovo and the mining town of Thorez in the Donetsk region of eastern Ukraine. Air-traffic controllers lost touch with it at 4:20 p.m. local time, pravda.com.ua reported.

The Vkontakte account reported at 5:37 p.m. Moscow time (4:37 in Donetsk) that a large plane —identified as an Antonov An-26 transport plane — "has just been shot down near Snizhne," a town close to where the Malaysia Airlines plane went down. This appears to be an edited version of a gloating post that is available only in screen shots now (I have one). In that initial version, the post went on: "We warned them not to fly in our skies. And here's a video of another bird going down. The bird fell behind a coal heap, residential areas were not hit, peaceful people did not suffer."