Rivals agree on type of missile, but who fired it?
While Russia and Ukraine trade blame over the shooting down of the Malaysian airliner, they appear to agree on one thing - the type of Soviet-era missile used.
But if an SA-11 Buk missile, known as "Gadfly" in Nato, struck the aircraft, that won't solve the mystery of who did it.
Russia, Ukraine and Russian-speaking rebels have all claimed the missile in their arsenals.
Circumstantial evidence points increasingly to the separatists, Western officials and analysts say, pointing to rebel claims of shooting at Ukrainian military aircraft at about the same time.
The rebels were believed to have used a similar system to shoot down a Ukrainian Antonov AN-26 aircraft on Monday and a military plane was shot down on Wednesday. Whether the 1970s-era radar-guided missiles would have been supplied by Russia or captured from Ukrainian forces is uncertain.
"Even if we know the weapon type, it is impossible now to say where it came from," said Samuel Charap, a former US State Department official and now a fellow at the International Institute for Strategic Studies in Washington.
On June 29, Russian newswire ITAR-TASS quoted separatists in Donetsk in eastern Ukraine, not far from where the plane went down, as saying they had seized control of a missile defence unit equipped with the Buk system.
But Moscow suggests Ukraine was responsible. The RIA Novosti news agency in Moscow quoted a source as saying a Ukrainian army battalion had a Buk system deployed near Donetsk a day before the crash and the missile probably came from that system. The source said the anti-government forces in eastern Ukraine do not have the Buk system.
If rebels were at the helm of the Buk system, they were probably not well trained in its use and may have misidentified the Malaysian Boeing 777 as a Ukrainian military plane, Charap said.
"It's the kind of scenario that becomes much more likely when you give a lot of undertrained and unreliable people sophisticated weaponry," he said.
Nick de Larrinaga, an analyst at IHS Jane's Defence, said that shoulder-fired missiles typically used by separatist rebels in eastern Ukraine would not be able to hit a passenger aircraft flying at normal cruising altitude.
Such weapons have shot down several Ukrainian helicopters and aircraft.
But he said a commercial aircraft would have been in range of surface-to-air missile systems such as the Buk or alternatively the Russian-made S-300, also called the "SA-10 Grumble".
"Both Russia and Ukraine have such surface-to-air missile systems," he said.