The biggest clue so far into who may have shot down Malaysia Airlines Flight 17 might be what Ukrainian officials say are intercepted communications between pro-Russian separatists operating in eastern Ukraine. The recordings, translated and distributed by Ukrainian officials, begin with an alleged militant informing others that a plane has been shot down.
Murder In The Sky: Malaysia Airlines Flight MH17
CNN: ‘We have just shot down a plane’ – alleged phone call

Ukraine's national security department SBU intercepted several phones calls between Russian military intelligence officers and members of the Russian-backed Cossack militants.