GLOUCESTER TOWNSHIP — A South Jersey police officer was charged with assault and suspended after slapping a 13-year-old girl twice in the head even though she was already in handcuffs.

John Flinn, 27, struck the girl after she was arrested on March 8, according to Camden County Prosecutor Mary Eva Colalillo.

Body cam footage that the county prosecutor released to New Jersey 101.5 shows the girl being restrained as police enter what appears to be an office. The video cuts to the girl face down on a box with her arms behind her back.  Flinn slaps her twice on the side of the head and then pushes her head down as he tells her to "stop resisting."

"I'm not!" she cries out.

The video clip does not show what events led to the slap. Prosecutors said she was cooperating with police at the time of the arrest.

The prosecutor did not disclose the circumstances of the disturbance but said the girl was not charged with any crime.

The officer was investigated by the department's internal affairs unit before the case was referred to the prosecutor, according to an affidavit of probably cause.

Flinn was suspended by Gloucester Township Police Chief Harry Earle and charged with simple assault.

Colalillo said the 13-year-old girl was checked over at a hospital and released.

Mayor David Meyer told NBC Philadelphia that he believed the incident happened at a group home.

Contact reporter Dan Alexander at Dan.Alexander@townsquaremedia.com or via Twitter @DanAlexanderNJ