> But having said that, there's an element of the social contract at play here. The exact same logic this guy is using suggests that he also shouldn't answer the questions of police investigating crimes in his neighborhood. "Have you seen this man? We think he just shot up your neighbor's car."

I believe this is different. In this case, true, you have no legal obligation to answer a cop's questions when he is investigating a crime. But I do think you may possibly have a moral obligation and answering his questions is part of your civic duty.

However, I don't really see any such obligation here when they are treating you as the suspect. There is no concrete reason for them to suspect you in the first place, other than their blind, blanket suspicion of everyone.