Considering how often we see terrorists masquerading as cops in other countries, this is relevant.

In South Florida, seemingly an incubator of law-breaking innovation, police impersonators have become better organized and, most troubling to law enforcement officials, more violent. The practice is so common that the Miami-Dade Police Department has a Police Impersonator Unit.
http://www.nytimes.com/2011/05/29/us...imes&seid=auto