The Justice Department's decision to not prosecute a civilian neighborhood-watch volunteer for a hate crime in the shooting death of an unarmed black teenager isn't necessarily a harbinger of how it will rule in two other high-profile deaths of unarmed black men at the hands of police.

Legal experts say that's because the standards used to gauge the existence of a hate crime committed by civilians are different from those used to measure the behavior of police officers.

Because George Zimmerman was not a police officer, the experts say, the Justice Department could only prosecute him for fatally shooting teenager Trayvon Martin nearly three years ago if it had sufficient evidence the killing was motivated by racial bias or hatred.

The department determined there was insufficient evidence to prove that.