Charlotte-Mecklenburg police say officers did not violate department policies in the case of a young woman who strangled herself in the backseat of a police cruiser.

Police launched an internal investigation two months ago into officers' actions involving 18-year-old Tanisha Williams, who remains brain dead after wrapping a seat belt around her neck in a cruiser with officers nearby, apparently unaware of what she'd done.

On Dec. 5, Williams was accused of stealing a $14 shirt from the Citi Trends store on Freedom Drive and then arrested.

She reacted violently, and when she was placed in the backseat of a Charlotte-Mecklenburg police cruiser, she began screaming and banging her head on the side window.

The incident was caught on tape by the cruiser's dashboard camera. In the video, Williams is seen banging her head against the Plexiglas divider.

After she began banging her head, police said Tuesday, officers went to get a restraining device from a nearby vehicle. It was during that time that Williams "deliberately wrapped" the seat belt around her neck - an action that investigators said took her less than 13 seconds.

"By the time the officers retrieved the device, Ms. Williams had stopped banging her head against the glass and the device was no longer needed," police said in a statement.

Police said officers opened the cruiser's rear door "at various times" to ask her questions and check on her well-being.

She didn't respond, police said, but officers saw her breathing.

"Due to dark night-time conditions and Ms. Williams' hair, officers were unable to detect that Ms. Williams had wrapped the shoulder harness around her neck," police said. "Officers continued to ask Ms. Williams questions and after not getting a response from her, officers shined a flashlight on Ms. Williams' face and were able to see that the shoulder harness was wrapped around her neck."

That's when they cut off the seat belt, removed her from the car, "rendered appropriate medical attention" and called paramedics, police said.

Williams' attorney, William Harding, said he wasn't surprised by the investigation's findings, but he maintains that the officers' actions that night violated their policies and procedures.