There were conflicting claims of responsibility after the shocking incident, but experts have suggested three possibilities: Pro-Russia separatists in Ukraine, Russian troops across the border, or Ukrainian government forces.
1. Pro-Russia separatists in Ukraine
The pro-Russian insurgents have emerged the prime suspect. Reuters reported a US official saying that Washington strongly suspected that the Boeing 777 was downed by a sophisticated surface-to-air missile fired by Ukrainian separatists backed by Moscow.
The plane crashed near the village of Hrabove about 40 km from the border with Russia near the regional capital of Donetsk, an area that is a stronghold of rebels who have been fighting Ukrainian government forces for several months. The incident came after a string of earlier incidents blamed on the Ukrainian separatists, including the downing of several Ukrainian government helicopters and a Ukrainian plane.
Social media posts by the insurgents - most of them hastily removed after the crash - also suggest the rebels thought they had shot down a Ukrainian army plane before realising in horror that it was in fact a packed Malaysian commercial airliner.
The rebels first claimed to have downed at least one Ukrainian army plane over the strife-torn eastern rustbelt on late Thursday afternoon. The VK social networking page of Igor Strelkov - "defence minister" of the self-proclaimed Donetsk People's Republic - first announced: "We just downed an An-26 near (the town of) Torez". The post also said: "And here is a video confirming that a 'bird fell'."
The website then provides a link identical to that published by Ukrainian media in reports about the Malaysia Airlines jet. The video shows locals referring to the same coal mine in the region mentioned by Strelkov.
Strelkov - a man of mystery with at least three names - is said to be a serving Russian colonel in Moscow's GRU military intelligence agency - a charge firmly denied by Moscow. He commands pro-Russian forces now in control of Sloviansk in eastern Ukraine, but his enemies suspect he is a direct agent of the Kremlin. The secret service in Kiev claims his real identity is Igor Girkin, reported the Daily Mail.
Ukrainian intelligence says Strelkov - dubbed "Igor the Terrible" - crossed the Ukrainian border in February this year, when the Crimean parliament was seized. He was blamed for the kidnapping of several peacekeeping observers from the Organisation for Security and Co-operation in Europe, said the Daily Mail.
Ukraine's Security Service also released what it said was an intercepted telephone conversation in which a rebel leader admitted to shooting down MH17, reports said. The recording, which was released with a transcript on YouTube, purports to be between Igor Bezler, the commander of rebel forces in the town of Horlivka, and a man identified as Vasili Geranin, a colonel in Russia's GRU military intelligence agency, media including the London Telegraph reported.
Speaking in Russian, the voice identified as Bezler's informs "Geranin" that an aircraft has been shot down and that a team has been sent to inspect the wreckage and search for survivors. Later, two other men - using the noms de guerre "Major" and "Greek" - are heard discussing the discovery that a "100 per cent civilian" aircraft was shot down.
"I'm only where the first bodies fell," Major tells Greek. "F***, the debris fell right in people's gardens. There are civilian things - medicine, towels, toilet paper."
"Are there any documents?" asks Greek.
"Yes," says Major "of one Indonesian student".
Further fuelling speculation that the separatists were responsible for the incident, ethnic Russian rebels in Ukraine claimed last month that they have "captured" a few BUK ground-to-air missile systems from the Ukrainian military, although the Ukrainians never reported any such losses. The missiles, also known in the West as the SA11, are big but highly mobile, and can reach to altitudes of 14km.
Leaders of the rebel Donetsk People's Republic, however, have denied any involvement in the incident.
2. Russian troops across the border
Western officials were also investigating the possibility that the aircraft was downed by the Russian military, launching an SA-11 missile from the Russian side of the border to support the separatists, said the New York Times.
A US official, who declined to be identified, said that the Russian military has two surface-to-air missile batteries positioned close to the border, reported NYT. But that there was no conclusive evidence that those batteries fired the shot that brought down MH17.
3. Ukrainian government forces
Leaders of the rebel Donetsk People's Republic claimed a Ukrainian air force jet had brought down MH17. But Ukraine's President Petro Poroshenko, who called the incident a "terrorist act", said he "could not exclude" that the plane was shot down by the insurgents.
Source: AFP, Reuters