First of all I'm glad no one I know was personally injured. I have friends who work at the Marathon, work nearby, tend to spectate the event, etc. As it happened, none were where the bombs went off. I'm sorry for those who were killed and hurt and hope they can find the healing and help they're going to need.
The lockdown that happened around the crime and subsequent pursuit and capture of the suspects was unprecedented. One estimate I saw said that the region will lose something on the order of one billion person-hours of productive work, leisure, etc. due to the lockdown, once it's all over. As I write it's still not done as there are buildings and areas of the city people are forbidden to enter. If the criminals' goal was disruption they succeeded that in spades. I can't think of another event of similar magnitude that spawned this kind of overreaction and it's a civil liberties disaster.
That said, there are two possibilities still at play. One is that this is a home-grown pair of people (or maybe more) who happen to have Chechen backgrounds. Coincidence is always possible, but it was no coincidence that the 9/11 hijackers were Saudi nationals. That was a message and it's possible someone was sending a message with this act. The other possibility is that what we have is the first sign that the Chechen resistance is taking its fight to US shores, in which case we have a far more serious problem. The Chechens are the ones who took whole schools hostage and shot hundreds of children; they're the ones who dropped bombs in crowded shopping malls. These guys are brutal and do not care one iota about whom they target. The Russians more or less stamped out their uprising through an even-more-brutal campaign of ethnic targeting, rape, starvation, torture, and wholesale military action that devastated (among other things) the vast majority of the capital of that province. Those techniques (fortunately) are not available in the US which might give someone the idea that over here is the place to move.
So if you're considering exporting your terror war somewhere and you see that at the first sign of trouble the entire fucking state locks down tight and your boys get hunted like rabid dogs until they are dead or bleeding on life support in a hospital then you might think twice about where you export your terror war. Terrorists by nature look for soft targets. Whoever decided on the lockdowns in MA was sending a very clear message not just to the people of the state but to anyone who might happen to be watching.
By now I'm assuming my general readership is educated and literate enough to realize that life is not CSI. The fact that Dzhokhar Tsarnaev is being interrogated without being Mirandized is not illegal. It just means that whatever statements he might make cannot be introduced in court against him.
The Obama administration has been puffering about a "public safety exception" to the need to inform prisoners of their Miranda rights, which I think is an extremely bad idea. In the hours after the chase, or after his capture, that might have held water but as days went by and the police themselves issued statements that "the danger is past" it's looking more and more like the administration is weaseling and trying to use a loophole.
It's possible they have more than enough evidence to convict him without his own statements. There will be physical evidence, witness testimony, and rumor has it that the two brothers made statements to the carjacking victim that may even have included admitting they were the bombers. If the government can win without ever putting Tsarnaev or his post-capture statements into evidence then there's no need to give him Miranda warnings. Failing to mirandize him is sending a signal, too, and it's an awful one. It's a signal that the Administration continues not to give a shit about civil liberties. Every prosecutor who takes a high-profile case has to stand up in front of the press and argue that she's got a winning hand. So why has the administration not come out now and say "We have enough evidence we can convict him without his own statements so therefore we don't need to give him Miranda rights."
Of course, if they think that they have more than enough evidence then there's no reason not to give him Miranda warnings, either. But that's logic and this is not about logic; it's about theater.
(I should note that there's a lively debate among legal scholars as to what, exactly, Miranda v. Arizona actually requires. My view is certainly not universal - see for example Professor Sandy Levinson's post on this topic at Balkinization.)