Abbotsford police are recommending an assault charge against a Williams Lake, B.C., RCMP officer after a 17-year-old girl was allegedly injured while in police custody.

The girl's mother, Martina Jeff, told CBC News her daughter was punched in the face by an RCMP officer while she was handcuffed in the back of a police car in September 2011.

Abbotsford police Const. Ian MacDonald announced the charge recommendation Wednesday.

He said the investigation was challenging because few people were paying attention to what was happening in the cruiser.

"The incident, ultimately, took place in the back seat of a police car and that back seat was in darkness and even though there were people around that police vehicle, not everyone's eyes were on that back seat and what was transpiring there."

At a news conference Wednesday afternoon, Williams Lake RCMP Insp. Warren Brown called the news disappointing.

He said the constable is on administrative duties until Crown counsel decides whether to lay charges.

An internal RCMP code of conduct investigation is also underway.