American officials, who said a surface-to-air missile was responsible for shooting down a Malaysia Airlines Boeing 777 on Thursday, said they suspected that the missile was either an SA-11 or SA-20, both Russian made.

In the early hours of the investigation, determining clear accountability for a missile attack was impossible, in part because all three of the forces in or near the conflict area — the pro-Russian separatists, the Ukrainian military and the Russian military — could possess SA-11s, which are one of many legacy weapons from the Soviet Union circulating through this war.