Reuters has a scoop this afternoon that supports the most widely held theory about the downing of flight MH17 (namely, that rebels using a Russian-supplied missile system fired at the plane by mistake, believing that it belonged to the Ukrainian military):
A powerful Ukrainian rebel leader has confirmed that pro-Russian separatists had an anti-aircraft missile of the type Washington says was used to shoot down Malaysia Airlines flight MH17 and it could have originated in Russia.
In an interview with Reuters, Alexander Khodakovsky, commander of the Vostok Battalion, acknowledged for the first time since the airliner was brought down in eastern Ukraine on Thursday that the rebels did possess the BUK missile system and said it could have been sent back subsequently to remove proof of its presence.
Reuters' story is datelined in the city of Donetsk, and the implication of Khodakovsky's statements seems to be that rebels in Donetsk province received the BUK system (which is apparently also called the SA-11 system) from other rebels in Luhansk province before the crash occurred, though he doesn't quite say so directly or definitively. (Read the whole piece to see what we mean.)
Kodakovsky believes the Ukrainian government may be complicit in the attack on MH17 because it launched airstrikes in a region where it had reason to believe anti-aircraft missiles were present and thus potentially provoked the counterstrike that downed the plane.