I'm not from the USA, but I'm sure you read enough news to know crimes of that nature also occur outside your country...ever heard of Europe, Canada, Australia...anyone ever told you women get raped and people get robbed in those countries too? I can assure you it happens.
But, and I'm sure it's the same where you live, if people are convicted of rape or robbery, they wouldn't simply show a conviction for impersonating a police officer.
People impersonate police officers for lots of reasons....people also have been known to walk into bathrooms and pretend they are police to stop drug use in there from continuing. You shouldn't assume it's the worst case scenario...speculation is dangerous...please wait for the facts.