First of all, I don't care about the psychology of the Boston jihadists – whether the older one put pressure on the younger one, etc. All we need to know is that they were jihadists, and therefore our enemy. Period.
What I do find myself preoccupied by is the psychology of those Americans who, even before the perpetrators were identified, hoped against hope that they weren't Muslims – and who, after the perpetrators were identified, were quick to assure us that Islam had nothing to do with it. Or who argued that, even if the brothers were motivated by Islam, that little detail doesn't matter, and we shouldn't focus on it.
I'm fascinated by the mindset of those who sought to obscure the vital moral distinctions in this case by waxing philosophical about such matters as the complexity of human character and the power of history. For example, David Remnick, in the New Yorker, described the Tsarnaev family as "battered by history…by empire and the strife of displacement, by exile and emigration." Many commentators strove mightily to make the case that, in the final analysis, we're all equally guilty and all equally victims.