Well, that breaks down a bit when you consider what 'conscience' is all about--and it can definitely involve ideology. I'll preface this by making it clear that I personally think the act of detonating those bombs was truly unconscionable. But, if someone truly has an allegiance to a Higher Power (and that's a big IF), and IF they truly believe that Higher Power is/was commanding them to attack a designated 'enemy,' then, FOR THEM, they might suffer their own sort of weird guilt for NOT doing what they felt had been defined as glorified and 'right' for them to do. IOW, your ideology (especially if it's a theology) defines your sense of right/wrong. Example: Joshua in the Old Testament and the conquest of Israel ('the Promised Land') from all the Hittites, Midianites, and other-ites living there. Joshua was and is revered as a man of God by Jews and Christians alike today. But I bet, if any of those [presumably escaped] Hittites had Internet, there may have been some moms and grandmoms chatting up their message boards about how they didn't see how "anyone who could attack and plunder their city, killing men, women AND children, could 'have a conscience.'"
The Tsarnaev brothers may or may not have had sociopathic tendencies - but the fact that they also had a religious ideology muddles the question a bit for me as far as determining if they had any conscience whatsoever. JMHO
