Lots of unanswered questions, but it really is surprising to me how political this has gotten. We know the background of these young men -- immigrated from Kyrgyzstan, have lived in the USA for many years and are naturalized citizens. The younger, still living, was known as a very typical young man -- not known to be religious, friends say he barely had an accent, and didn't seem to have strong ties to his older brother either. Seems that the older brother was a little more aloof.
I doubt that them being Chechen has much to do with it, though there is some very unconfirmed evidence that they may have been "radicalized" religiously (yes, Islam) in the recent past. The uncle, whose credibility is certainly up for debate, claims that there is very little those two could really know about their ethnic home in Chechnya since they have spent no time there.
In terms of security, etc...there are two sides. On one hand, I'm glad that they have to use these crude, homemade devices to do this kind of damage. There's no way we can really prevent them getting the objects needed to make that bomb. They didn't have guns nor sophisticated weaponry nor poisons nor anything else that could have made them more dangerous. They didn't fly a plane into the marathon. There were tons of roadblocks if their intent was maximum lethality.
While there are roadblocks in their way to commit these acts, it's always possible that people can hurt other people. The most sophisticated, most lethal methods and plans can be foiled or hampered -- that's great. However, the reason these more crude type of acts aren't done more often speaks to the goodness of our people. Any one of us could inflict mass harm, but we don't because we don't want to. The people that want to do these things could very well be counted on one hand, and that is part of the reason these attacks are so rare. Human goodness can prevail and usually does.