Police may offer a reward for help finding the person who threw two bottles of acid from a Mong Kok rooftop on Saturday, injuring 46 people. An officer involved in the investigation said this yesterday as the security chief appealed for information to assist in what he said was a difficult investigation. The bottles, thought to have been tossed from the roof of the Yuen King Building at about 5pm, crashed into the busy pedestrian area of Sai Yeung Choi Street South, which was packed with Christmas shoppers. The injured were treated in hospital and discharged the same day. Secretary for Security Ambrose Lee Siu-kwong said the government was very concerned about the incident and police were conducting a thorough investigation into the case. 'I am making an appeal. If residents have any information in connection with the incident, they can contact the police,' he said. He also said it was meaningless and irresponsible to 'harm others to benefit nobody'. Three teams of officers from the Mong Kok police station, including an anti-triad squad, have been assigned to investigate the case. 'This shows that we are very concerned about the incident and we need more manpower because we have to interview 46 victims and talk with witnesses and residents,' a police source said. Plain-clothes officers returned to the scene at about 11am yesterday and talked to residents. They remained tight-lipped over the probe as they left the scene. A police spokesman said that so far, no one had been arrested in connection with the case and the investigation was continuing. The incident took place in the same area of the bustling district where bricks were thrown from high-rises on 12 occasions between August and October in 2004. Police arrested a 42-year-old pimp in October of that year. He was sent to jail for 21/2 years in March 2005.