The Police Ombudsman's Office has appealed for information about an incident in the Pennyburn area of Derry/Londonderry in the early hours of 23 July 2012.
It happened at around 5.45am as police arrested a man at a party at a house in Pennyburn Court.
Anyone who saw what happened is asked to contact the Police Ombudsman's freephone information line on 0800 032 7880.