From Washington to Moscow, via London, Brussels and Amsterdam, intelligence analysts will be studying data and imagery to find out how and why Malaysia flight MH17 came down in eastern Ukraine.
The Pentagon has a number of satellites covering the area. They have been constantly monitoring ground activity since Ukrainian/Russian relations broke down so dangerously months ago.
Their analysts will be looking for two things: a flash of light indicating a missile launch and/or an ultra-violet trail. If they can identify either, they should be able to track the trajectory of a missile and triangulate a launch site.
A UK E-3D Sentry aircraft is operating under NATO orders in the region monitoring Russian and rebel movements.
If that had been in the air and within roughly 200 miles of the location, then it would have picked up activity. My understanding, however, is that it wasn't flying at the time.
If the plane was shot down, who did it, and how?
MANPAD, shoulder-borne anti-aircraft missiles favoured by guerrilla groups around the world, have a range of about 15,000ft (4,572m). They are best used against low-flying aircraft with high heat signatures - helicopters, for example.
They have been used to target commercial aircraft, but only during take-off and landing.
MH17, four hours into its flight, was at a cruising altitudes of 30,000ft+ (9,144m). Well out of range.
The most probable weapon is what NATO call "the Grizzly", the SA-17 Buk 2. This was designed and developed by the Russians back in the Cold War. It is fired from what is essentially the back of a big truck.
Both the Ukrainian and Russian militaries own Buk systems. MH17 would have easily been within range.
But unlike MANPADS, which track targets using heat, the Buk uses radar, meaning that anyone operating it must be well-trained - this backs up the idea of state-lent soldiers to support the rebels.
Could this have been a mistake? Very possibly, even probably.
Strategically you have to wonder what any of the possible suspects - Russians, Ukrainians, rebels - have to gain by shooting down a Malaysian passenger plane.
One early theory is that the target could have been a Ukrainian military plane. If the missile missed it might have locked onto an alternative source. A bit far-fetched maybe, but not to be discounted just yet.
Civilian aircraft are easy to identify. They broadcast a squawk which would be picked up by any weapons system trying to "paint" or lock on to it. They also fly well-known, clearly defined routes.