The BUK surface-to-air missile system believed to have shot down Malaysian Airlines flight MH17 is an old Soviet-built weapon designed to engage aircraft, cruise missiles and drones that is still widely used in eastern European states, including Ukraine.
They are capable of taking down aircraft the size of a Boeing 777 flying at a cruising altitude of 33,000 feet, meaning the intensity of the impact is likely to have blown the plane apart in the sky.
Witnesses says wreckage and body parts of the passengers and crew are scattered over an area of around nine miles, reinforcing the idea that the plane broke up mid-air.
BUK missile systems have large self-propelled launchers that use radar to engage aircraft or missiles up to an altitude of 75,000 feet.
A launcher similar to the BUK missile system was seen earlier today by journalists near the eastern town of Snizhne, which is held by pro-Russia rebels.
The BUK, developed by the Soviet Union in 1979, has remained widely in use throughout the former Soviet states, including Ukraine.
Until then it was assumed the only surface-to-air missiles in rebel hands were shoulder-held launchers with a maximum engagement range of 10,000 feet.
In a statement Donetsk separatist leader Andrei Purgin said that he was certain that Ukrainian troops had shot it down but gave no explanation for that statement.
Purgin said he was not aware of whether rebel forces owned BUK missile launchers, but even if they did, there had no fighters capable of operating it.