A 56-year-old central Alberta man is accused of pretending to be a police officer and then kidnapping and sexually assaulting a teenage girl.

Gerard John Baumgarte of Red Deer was charged Monday with impersonating a peace officer, kidnapping with a firearm, sexual assault, aggravated sexual assault and uttering a threat, said the RCMP.

The victim, 16, vanished from the town of Penhold, about 120 kilometres north of Calgary, on Thursday evening. She was last seen at a convenience store buying juice for her sore throat.

'Nobody has a red-and-blue flashing light … without planning that ahead of time. It's not coincidental.'—RCMP Sgt. Patrick Webb

Her family found her truck parked in front of their home with the keys inside and the lights on. Her purse and the items she bought at the store were in the truck, but her wallet and cellphone were gone.

Investigators believe the girl willingly went with the man because he was dressed like an RCMP officer and had flashing blue and red lights in his vehicle similar to those used by police, Sgt. Patrick Webb said Monday.

"There's planning in this, and that's what's going to be coming out in court," Webb told reporters. "Nobody has a red-and-blue flashing light … without planning that ahead of time. It's not coincidental."

The girl managed to escape her captor at a Red Deer mall and phone her parents on Saturday afternoon, 46 hours after she went missing, said police.

The teenager's photo was released shortly after she went missing, but her name and identity are now protected under law.

RCMP Sgt. Patrick Webb advises members of the public to ask a police officer for ID or call the 911 dispatcher for verification if they're unsure of the officer's identity. (CBC)

Webb said it's extremely disturbing that someone would impersonate an officer and shake the trust that is shared between the public and law enforcement agencies.

"To have this happen, it is quite disturbing because that person, who is in this case victimized, has put her trust in what she believed in for years and years. To have that actually destroyed like this is quite, quite disturbing," he said.

Baumgarte, who has no criminal history, remains in custody, said Webb.

The RCMP is asking members of the public to report whether they have run into a circumstance involving someone impersonating a peace officer. That term applies not only to police, but also to officials such as jail guards and game wardens.

If you're not sure about the validity of an officer, Webb advised that people remain in their house or vehicle and ask for ID or a badge. If they're still not satisfied, they should call 911 and get the dispatcher to verify the officer's identity.

"That person, if they are a peace officer, would be content to wait as is such time as it's confirmed," said Webb.

"We really want to stress to the public that any instance of impersonation of a peace officer is very rare."