(CNN) -- A Wiltshire, England, police sergeant could face prison time at his sentencing Tuesday for assaulting a 57-year-old woman in custody two years ago, an incident caught on the station's closed-circuit television.
The woman sustained an injury to her face in the 2008 incident at Melksham Police Station in Wiltshire, Assistant Chief Constable Patrick Geenty said in a statement Sunday. Although police did not identify her, the victim, Pamela Somerville, has given media interviews.
"We are extremely concerned when anyone is injured whilst in our custody and the court has decided that this injury was as a result of a criminal assault by Sgt. Mark Andrews, a member of Wiltshire Police who was performing duty as a custody sergeant at the time," the statement said.
"We respect the decision of the court and Wiltshire Police has formally apologized to the injured lady for the assault she suffered whilst in our care."
On the footage from the police station, released over the weekend, Andrews is seen dragging Somerville across the floor and throwing her into a cell, where she lies motionless for a moment before struggling to her feet as blood drips from her head onto the cell floor.
"I thought I was going to die," Somerville told the BBC, "by people that you trust. You can't imagine it. They're the people that you trust, so who do you trust after that?"
The incident was reported by another officer at the station "who was concerned at what had taken place," the police statement said. "The officer found herself in a very difficult situation created by her own supervisor but performed her duty in accordance with the highest standards expected of a police officer in bringing this unacceptable incident to the attention of another supervisor."
Andrews was removed from public duties as soon as the supervisor was made aware of the incident, and police referred the matter to the Independent Police Complaints Commission, which decided an investigation should be conducted by Wiltshire police. That resulted in a file being sent to the Crown Prosecution Service, which led to Andrews' trial.
Following his conviction on July 30, Andrews was suspended from duty immediately. An internal police conduct hearing is set for next month.
Since the incident occurred, more than 30,000 people have been in Wiltshire custody centers, and "during that time, there have been no other serious assaults of this nature," police said. Although there have been 13 complaints of assault, none have been substantiated after being investigated.
"Some 16,000 people are dealt with annually within police custody centers in Wiltshire and the public will understand that this environment can be very difficult, with hostility, conflict and violence towards staff often occurring -- although these conditions can never excuse or condone any form of unacceptable or unlawful behavior by police officers or police staff," the statement from Geenty said.
Since the incident, Wiltshire police have undergone four independent inspections with favorable reports.
Somerville was lawfully arrested on suspicion of drinking and driving, and refused to take a test. She was not charged with any offense, police said.
"The incident should not have happened, and I am very sorry that we let this lady down," Geenty said.
CNN's Bharati Naik contributed to this report.