The Boston Marathon Muslim bombers (see what I did there?) were identified and corralled relatively quickly. The reason for the quickness is this: Outbreeding.
To put it more conventionally, a cultural-cum-genetic predisposition toward love-based monogamous marriage that strengthens outbreeding and restricts inbreeding is what helped authorities identify and track the bomber suspects.
By limiting inbreeding, a phenomenon which usually occurs via cousin marriage, the circle of trust is widened. When police ask for tips, this built-in higher level of trust is effectively an enlarged witness pool, ready to jump in with assistance.
Clannish societies, like Chechnya, are more inbred societies. People there look out for family first, the general public good a distant second. Had the Chechen Muslim brothers (see what I did there again?) committed their murderous act in Chechnya, where clan blood is thick and civic-mindedness is thin, it is likely that they would be on the run for a long time, because family members, 2nd, 3rd, or 10th removed, would be all omertá and the cops, such as they are, would get nothing but cold leads.
America has, until lately, been an outbred society (but still mostly inbred as a continental race). White Americans are mutts of mixed Northwest European ancestry. The circle of trust is generally huge in Anglo nations, and that’s why cops can do their jobs there. Family is still important, but there’s a greater degree of cooperativeness and fellow-feeling than would be found in places like, say, Iraq.
That of course, is all ending now. Diversity and the resentful enclaves spawned in its wake are destroying fellow-feeling. Clannish people are setting up shop in the most American of towns. Cognitive and cultural stratification as described by Charles Murray in Coming Apart is further contributing to the shrinking circle of trust.
Soon now, very soon, the day is coming when future Tsarnaev brothers will get to enjoy a life on the lam in America for many, many years, protected by inner circle insiders who don’t give a shit about the fate of America as a cohesive nation.
PS One curse of outbreeding: Pathological altruism. The kumbaya genes spread out of control until wishful thinking, instead of reality-based thinking, push the stricken population into self-destructiveness.