If he gets life without parole, within two years (before Obozo leaves office), some prominent American or Americans will get kidnapped by some slimeball Islamist operation and will be threatened with death unless Tsarnaev is released in a trade. And if unsuccessful, that approach will be tried over and over again.
Since he cannot be sentenced get live without parole taking care of pigs in a grange; the sentence should be death in a coffin with pig skin to make sure he goes to hell.