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A nine-year member of the RCMP has pleaded guilty to the assault of a prisoner in his care. The charge stems from an incident caught on cell block video in which the constable is shown assaulting the prisoner at the Lac La Biche RCMP detachment on Sept. 13, 2009.

The surveillance video played during court proceedings Friday, which has no audio, shows two RCMP officers just starting their shift, and leading the prisoner down the hall. The 33-year-old prisoner, who had been unruly and injured in a bar fight hours earlier, believed he was supposed to be released from custody.

The video shows Constable Desmond Sandboe lunging at 33-year-old Andrew Clyburn and appears to smash his head into the wall twice. The prisoner is then sent to the ground with the constable swinging his hand towards the man's head.

During this time, two other men can be seen standing behind the constable and the prisoner watching the assault.

After 40 seconds, the prisoner is led back to his cell.

The incident was reported to the RCMP Detachment Commander who then referred it to the Alberta Serious Incidence Response Team (ASIRT), a police body that investigates incidents or complaints of serious injury or death that may have resulted from the actions of a police officer. ASIRT took over the investigation on September 16, 2009.

"The RCMP finds this incident appalling," said Supt. Joe Loran, acting commander with Alberta RCMP.

The court heard that Const. Sandboe filed a report after the beating claiming the prisoner lunged at him and that it was he who was assaulted.

The constable was originally charged with assault causing bodily harm but because his victim was already wounded, the Crown was unable to prove what injuries Sandboe might have inflicted.

The constable has been suspended without pay.

The Crown has not revealed what they will be asking for when it comes to sentencing.

The constable will be sentenced in January. The RCMP has a Code of Conduct investigation underway regarding the officer and this incident.

During court proceedings, it was not revealed what the prisoner said to the constable prior to the assault.

With files from David Ewasuk