Unanswered questions about MH17 crash show limits of US intel

ASPEN, Colo. — A series of unanswered questions about the downing of Malaysia Airlines Flight 17 shows the limits of U.S. intelligence-gathering even when it is intensely focused.

U.S. intelligence officials have used satellite imagery, intercepted conversations and social media postings to present what they call a solid circumstantial case that the plane was brought down by a Russian-made SA-11 surface-to-air missile fired by Russian-backed separatists in Eastern Ukraine.

But they have not offered proof that the separatists obtained the sophisticated missile system from the Russian government. And they say they have not determined what, if any, involvement Russian operatives may have had in directing or encouraging the attack, which they believe was a mistaken attempt to hit a Ukrainian military aircraft.

Finding such proof, they say, will take time. Moscow denies involvement.