I thought this was interesting regarding how they got the lead they needed to get the first of the murderers
Now as to why the bombers did it, how many there are, whether it's a political motive or just a group of losers (a lot of what does it in our country), those are the questions we won't know for awhile. Chechnya connection does not guarantee a specific motive. If they get some alive that's the only hope for an answer and not always then.
What interested me with this is once again it was an ordinary citizen, the man who lost both his legs, who as soon as he regained consciousness said he had seen the man's face who planted that bomb. His ID helped authorities get the photos out of the crowds.
So often I hear-- leave this up to the authorities, trained people, but so often, as with so many of the lives saved that day, it's ordinary people who know what to do and do it.
Hopefully soon they will have the rest of the killers whether it's just the one surviving brother or more involved in this plot.