Dealing with the young Boston terrorist is a difficult question given different objectives--justice for past crimes versus intelligence to prevent future attacks.
While I understand that if the older Boston bomber brother in his travel overseas essentially joined al Qaeda or another jihadi group, he could be considered an enemy combatant who waged war on us here, notwithstanding his American citizenship. But he is dead, so the question is moot.
The younger brother is clearly an American citizen, and it doesn't seem like he joined a foreign force. So I don't think he should be tried by the military as an enemy combatant. He is a citizen and should be tried in a civilian court. Perhaps treason is the appropriate big crime to be charged, under the circumstances.
That said, he needs to be questioned without lawyers to determine if there is more to know about the bombing and whether there are support terrorists involved but not caught. Luckily, it is possible to question him without spoiling the ability to try him as a civilian later.
So after that questioning, the younger brother should be tried in a civilian trial. I'm not in favor of civilian trials for foreign unlawful combatants. Indeed, I'm fine with them rotting in Guantanamo Bay. But a citizen who is not part of an enemy force--no matter how awful the citizen is--ultimately gets their day in court.
Heck, with a little prison poetry under his belt, his career path might open up in our higher education system, no?
But it is a difficult question. Which is why the Obama administration prefers drone strikes even abroad so questions of holding jihadis are moot.