(CNN)-- Two Mississippi killings that may have been committed by someone posing as a police officer have prompted police to give some unusual advice to drivers.
Authorities are asking citizens to be careful if they are pulled over and feel uneasy. They advise drivers to call 911 and verify that a legitimate officer is pulling them over or drive to a well-lit, crowded place before stopping, actions permitted under Mississippi state law.
In the Mississippi killings, police believe the suspect may have tricked drivers into pulling over on the highway.
The issue is obviously different from choosing not to pull over just to challenge police. But it begs the question: What can you as a citizen do if you have concerns or suspicions that someone might be impersonating a police officer?
Bill Johnson, executive director at the National Association of Police Organizations, said there are no standard nationwide laws or rules on the issue and every situation is different.
Johnson said that generally, if citizens have concerns, he believes they should try to pull over to a lighted area, or the most populated area they can, to feel more comfortable. But they can also be their own detective. Johnson said that generally, someone impersonating a police officer doesn't have a true marked car.
An impostor is more likely to be using a car that is similar to the look of patrol cars: Ford Crown Victorias or Chevrolet Impalas, for example. Often they will be legitimate police tucked away on a highway to catch speeders, but you're less likely to find an impostor with an actual stolen police car.
He said drivers should look for specifics: emergency light bars, vehicle decals and even a search light.
In cases such as the current one in Mississippi, Johnson said, police are likely to be more lenient with drivers who take more time to pull over.
"I think in a case like Mississippi where it appears that someone - it may be an active killer out there posing as police - it’s fine if the citizen who is being signaled tries to get on their own phone and call 911 to confirm that it is an actual officer," Johnson said.
And if it occurs in a state where there are laws preventing using your phone while driving, he expects that police would also understand if a motorist did so under circumstances such as in Mississippi.
"There’s gotta be some discretion in enforcement when it comes to these circumstances," he said. "If the person has some doubt about the validity of the stop, (or the) car doesn’t appear to be marked properly, I think its fine to try to confirm what’s going on around them. The real police officers in the jurisdiction would understand."