New York ? A man forces his way into an apartment to rape the woman who lives there. A guy on a bicycle handcuffs and robs pedestrians, and another gropes random women on the side of the road.

In each case, men pretending to be police preyed on victims who let down their guard because they thought they were being stopped by real officers.

Officer impersonation is a nationwide crime, and it has flourished in recent years with brazen criminals sometimes going to great lengths to pull off their ruse.

There are no readily available national statistics on the number of police impersonation cases, but it is enough of an issue to prompt some cities to take action.

New York City police arrest about 100 suspects annually on charges of impersonating an officer. The NYPD has a specialized unit, believed to be the only one in the country, dedicated to solving cases where a suspect impersonates an officer.

The unit analyzes statistics, uses DNA and other crime-solving techniques and even sets up sting operations, going undercover to investigate impersonators.