Chechen? American? Immigrant? Citizen? Muslim? Boston Marathon bombing suspects Tamerlan and Dzhokhar Tsarnaev may be all of the above, but how Americans attempt to come to grips with the attacks allegedly perpetrated by the brothers has much to do with how Americans identify them.

The brothers "don't neatly fit into pre-existing boxes," says Peter Spiro, an international law professor at Temple University. "It is a very complex picture," challenging the psychological need to "set the boundaries of the in-group and treat others differently."

For many Muslims, even the possibility that the perpetrators could be Muslim reignited the fear that all people of that faith would pay a price in the form of discrimination or retaliation or shame. "Please, don't be a Muslim" many tweeted in the hours before the suspects were pinpointed.