The thing about suits is its a signal that can be faked, if you have enough money. Perhaps that is why the mafia wear suits (source: TV), so it can help give the impression of being legitimate businessmen.

Sure, in extreme cases such as wearing gang colours or tats that gives a lot of information. But some gangsters wear suits, and not all crime is organised crime, and I'm sure that perfectly ordinary businessmen who have no gang affiliations whatsoever commit crimes sometimes.

In many circumstances race does give comparitivly little knowledge. Asian women commit violent crimes far less then black men, but if an Asian woman's fingerprints are on the murder weapon, then its her that the police should investigate.

On that note, there are also large differences between men and women. I am a man, but I concede that while it may be sexist for a woman to be far more worried about male assailants than female assailants, this behaviour is also perfectly rational. WRT domestic violence the police do automatically assume that the man is the perpetrator, which is more likely than not the case, but also leaves the system open to abuse if being male is considered sufficent grounds for arrest in absence of any supporting evidence.

The interesting thing about comparing the black/asian difference and male/female difference is that the side which supports discrimination based upon the difference is the left in one case and the right in the other, so its interesting to see whether people have a consistent opinion across both cases. One debate tactic is to counter "all men are potential rapists" and "men should be taught not to rape" is to compare with statements replacing sex with race, like "teach black people not to steal" in an attempt to expose underlying hypocrisy. Of course, these two cases are not exactly symmetrical.

For anyone approximating a Baysian reasoner, for more information to move you away from the truth is absurd. However, I do acknowledge that any discrimination on group based differences is open to abuse by those 'reasoning' in bad faith.