[R]esults from two experiments consistently show that individuals can tell who is a criminal and who is not, by indicating that they believe the actual criminals have higher probability of being a criminal than actual noncriminals.
However, their results also show that individuals cannot tell what type of criminals they are. While Valla et al. are initially puzzled by this finding, it is actually consistent with what we know from criminology. As I explain in an earlier post, criminals do not specialize. Men who commit one type of crimes are more likely to commit other types of crimes. (Remember O. J. Simpson?) Even though, for their experiments, Valla et al. carefully select pictures of criminals who are convicted of only one type of crimes, in empirical reality, there are no men who are only murderers (and do not and will not commit other types of crimes) or men who are only thieves (and do not and will not commit other types of crimes). Given time, some men would commit other types of crimes. In empirical reality, there are men who commit (all types of) crimes, and there are men who do not. And Valla et al.'s experiments show that individuals can tell them apart because the two types of men look different.
But it gets stranger, even downright creepy...
In both experiments, women are unable to spot rapists. Women consistently rate convicted rapists to be less likely to be criminal than not only other types of criminals but noncriminals as well! While this may be initially puzzling, upon further reflection, it makes perfect sense, as Valla et al. explain in their paper. In order to be a successful rapist, the man has to be able to fool the woman and earn her trust initially. Men who "fit the bill" by looking like a rapist or otherwise criminal and dangerous would not be able to do that. They would not be able to get close enough to the women to rape them. This may be why women, but not men, are unable to spot rapists, even though women are equally good as men at spotting other types of criminals.
If this is true, it would be a good reason for women to have trusted men around (brothers, fathers, etc.) who can detect the creeps for them.
Edit: I got 6 false positives, 4 false negatives, 10 correct negatives, and 12 correct positives. I missed one of the rapists. I did not actually make sure I checked 16, or do process-of-elimination just went with my gut, and ended up checking 18. What can I say? I'm suspicious.