“The Chechen idea fits. The rebels there are technically very good and tactically very sloppy. Like these guys.”
Sounds like once they complete the initial operation, they go into Rampage Mode very easily.
I doubt that teenagers (one of the perps was 19) just spontaneously decide to move to the US from Chechnya, bomb the Boston marathon, and start shooting police officers. Somebody trained them. Somebody financed them. Somebody sent them. Are there other cells around the country?
The question is, who is responsible? Iran? AQ?