Taipei - Families of victims killed during an explosion at a "colour party" in Taiwan that left 15 dead and hundreds injured are calling for the event organiser to receive a stiff sentence, as a procedural hearing opened in Taipei on Tuesday.In October, Lu Chung-chi, the owner of Color Play Asia that organised the event, was charged with negligence leading to death and injury and faces up to five years in prison. The accident occurred in June at the Formosa Fun Coast water park, just outside the capital Taipei, when clouds of multi-coloured corn starch sprayed on revellers ignited after heat from stage lights triggered a blast that ripped through the crowd. The event organiser appeared in a Taipei court on Tuesday as a four-day procedural hearing commenced, where relatives of victims gave testimony. Critical condition"[Lu] really destroyed our very happy family," the mother of Wu Yen-chieh, who died after 67 days in hospital, told the court. "Even if it's a death sentence I won't forgive him," she said, holding a portrait of her deceased daughter. Victims' families also expressed anger that of the nine people who were under investigation for the explosion, only Lu was charged."It's like piercing a knife through the hearts of the families," said the mother of Liu Chih-wei, who died six days after the disaster. Five months on, 28 people are still being treated in hospital with one in critical condition. Prosecutors found during their investigation that the corn starch powder, which was sprayed onto the crowd for effect ignited when it was sucked into the lighting system. Lu's trial date has not yet been set.