The bullet which killed a 19-year-old at a beach dance party last month was fired from a police gun, the public prosecutor's office has said.

Two other men who were injured at the Hook of Holland party on 22 August were also hit by police bullets. At the time it was unclear who had fired the shots.

The Sunset Grooves party got out of hand when hooligans from the Rotterdam area rioted and targeted the police. A number of partygoers in the 50,000 strong crowd were stabbed. Officers felt threatened by the situation and fired warning shots.

The national police investigation into events at the party is expected to last a couple of months, the prosecutor's office said. Some 200 witnesses are being heard.

A report drawn up by a police specialist from another force says that Rotterdam police chiefs made grave errors in handling the riot. The Rotterdam police are said to have known one day in advance that hooligans were planning to disturb the peace, yet no riot police were kept on standby. Rotterdam Mayor Ahmed Aboutaleb has meanwhile suspended one of the city's police commissioners because of his handling of the incident.

Rotterdam hooligan (YouTube screenshot)