Within hours of the F.B.I.’s release of the suspects’ photographs, we collected responses from 426 white Americans to a broad questionnaire assessing a range of their demographic information as well as aspects of their ideological orientations. Eight days later, we offered these same participants the opportunity to respond to a second questionnaire. Here, we presented them with the original F.B.I. photos, and asked them to tell us how white they thought the suspects looked.

We then asked the participants whether they endorsed statements such as “I hope the perpetrator of the Boston Marathon attacks rots in hell” and “It is O.K. for Tsarnaev not to have been read his Miranda rights before interrogation” and “We shouldn’t rush to judgment in bringing the perpetrator of the Boston Marathon attacks to justice.” They were also asked to indicate the sentence that they felt Mr. Tsarnaev ought to receive should he be found guilty, with options ranging from “a maximum of 20 years in prison with the possibility of parole” to “the death penalty.”

We found that there was substantial ambiguity about whether the Tsarnaev brothers were white. On a scale from zero (nonwhite) to 100 (white), the participants varied in their perceptions, with ratings running the full gamut from zero to 100. The average rating was around 64.

Which individuals were less likely to “grant” the Tsarnaevs whiteness? In our initial questionnaire, we focused on two ideological outlooks that have been well studied by political psychologists: the belief that some groups of people are superior to others (“social dominance orientation”) and the belief in the importance of following traditions and respecting authorities (“right-wing authoritarianism”). We found that participants who scored high in either outlook were less likely to perceive the Tsarnaev brothers as looking white, effectively steering the brothers into “outsider” territory.

We also found that such whiteness perceptions had the potential to play an important role in the outcome of Mr. Tsarnaev’s trial. The lower that individuals rated Mr. Tsarnaev as looking white, the more willing they were to punish him severely. In a case like Mr. Tsarnaev’s, where guilt is widely presumed and where the outcome will most likely fall on one side of the line between life imprisonment and death, this finding seems especially relevant.