A tax-related dispute might have provoked the arson attack at Revenue Tower in Wan Chai that led to the evacuation of about 600 office workers, a police source said yesterday. The 51-year-old man arrested in connection with the case owns a laundry, according to the source. 'We are looking into his background and business as part of the investigation,' the source said. 'We're also checking with the Inland Revenue Department to find out whether the suspect had a tax-related dispute with its staff.' Security was stepped up at Revenue Tower yesterday, with security guards checking visitors' identity and examining their bags at the ground-floor lift lobby. There are 12 government departments with about 8,000 employees in the building. The attack happened on Thursday when a man approached payment counter No5 at the Inland Revenue Department's business office on the fourth floor of Revenue Tower in Gloucester Road. He poured a flammable liquid onto the counter, wiped it with a towel and then used a lighter to ignite it before fleeing. There were about 10 customers in the tax office. The culprit's trousers caught fire and he put out the flames with his hands before running downstairs. He managed to escape in a taxi, although three members of the public gave chase in an attempt to get hold of him. 'The investigation shows that he poured flammable liquid from three plastic bottles. Three empty plastic bottles and a lighter were seized at the scene,' the source said. About 600 workers were evacuated from the lower floors of the tower. The sprinkler system put out the blaze before firefighters arrived. The suspect was arrested in Tuen Mun Hospital when he sought treatment about five hours after the attack. Police said the man suffered burns to his left leg and there were burn marks on his trousers when he arrived at the hospital. Last night, the man was being held in a custodial ward in Queen Mary Hospital. No charges had been laid.