Vance Boelter left the state of Minnesota in fear after he allegedly posed as a police officer and carried out the shootings of two state lawmakers, killing one and her husband, at their homes last week.

But what can you do to verify that the person who knocks on your door or pulls you over while you’re in your vehicle is a law enforcement officer?

Mark Bruley, chief of police in Brooklyn Park, Minnesota, where Boelter allegedly shot and killed Minnesota state lawmaker Melissa Hortman and her husband, Mark, told reporters at a press conference earlier this week that there’s one thing you can do that’s “never wrong.”

“You always can call 911 and verify if the person at your door is a police officer,” Bruley said. “If they are working police officer, they will be connected to a dispatch center that can validate that. So the first thing I would do is, if you’re concerned about it, is call 911. Obviously, there’s a lot of different uniforms, and it’s never wrong to do that.”

Higgins said officers usually call in traffic violations to dispatch, so drivers can still call 911 or the local police to verify that an officer performing their duties initiated the stop.

Higgins advised citizens to always be aware of their surroundings and to pull over in public places, if possible.

If unable to immediately pull over in a public place, Higgins said drivers can lower their window just enough, keep their car in drive and ask the officer if it’s possible to drive to another place that is safer or more public.

Higgins said that police officers understand that citizens may be uncertain or nervous and ask for verification.

“If their answer is anything other than professional, it should raise a concern,” Higgins said. That is, if the citizen didn’t do anything obviously illegal like run a red light, he added as a caveat.

In the case in Minnesota, Boelter allegedly impersonated a police officer, wearing a flesh-colored mask, a black tactical vest and carrying a flashlight before shooting and killing state Rep. Melissa Hortman and her husband, and wounding state Sen. John Hoffman and his wife, Yvette, at their respective homes.

Boelter also drove a black SUV equipped with police-style lights and a fake license plate that said “POLICE,” according to a court affidavit.

Video footage from Hoffman’s home shows a masked Boelter at the front door wearing the black tactical vest and holding a flashlight, according to the affidavit. Boelter then allegedly knocked on their door and shouted repeatedly, “This is the police. Open the door.”

The Hoffmans answered the door but, since Boelter was shining the flashlight in their eyes, realized too late that Boelter was not a real police officer, the affidavit said.