Slain engineering company boss answered his mobile phone moments before the explosion A businessman who had a narrow escape in a bombing attack about four years ago was killed by an explosive device that shattered his car in Tin Shui Wai yesterday. Liu Kwok-shun, 47, had just answered his mobile phone and was slowing for a traffic light on Long Tin Road about 8.30am when the bomb went off under his seat. His wife, Wong Lai-kiu, 42, who was sitting beside him, suffered severe injuries to her face and right arm, leg and body. The blast ripped a hole in the floor of the car under the driver's seat. The Mazda sedan careered out of control for about 10 metres before ramming the rear of another vehicle, police said. Police last night classified the case as murder and said the homemade device contained less than 500 grams of explosive. 'It was a powerful explosion,' Assistant Yuen Long divisional commander (operations) Chief Inspector Johnny Wong Mong-tong said. 'The force of the blast ripped a hole in the floor of the car under the driver's seat, which also broke into pieces. 'The roof bulged [out] and the two front doors were damaged and forced open. The windscreen and all the windows were smashed. The blast left a crater four centimetres deep in the road,' he said. Debris, including metal and glass fragments and human flesh, littered the road. Rescuers found Liu unconscious inside the car. His wife was still conscious but passed out soon afterwards. The couple was taken to Tuen Mun Hospital, where Liu was declared dead. His wife was in serious condition last night. Secretary for Security Ambrose Lee Siu-kwong insisted Hong Kong was a very safe city despite the bomb attack, which he described as an isolated case. 'We will not tolerate any act of violence ... that threatens the safety of our citizens,' he said in Guangzhou, where he was attending a conference. Chief Superintendent Ma Wai-luk, of the Police Public Relations Branch, said officers were still investigating whether the device was planted directly beneath the driver's seat. Police said that before Mrs Liu lost consciousness, she told ambulance crews that her husband had answered his mobile phone moments before the blast. 'We are investigating whether the blast was triggered by a mobile phone ringing or other reasons,' Chief Inspector Wong said. Investigators went to the car park of Tin Shui Estate in Tin Shui Wai, where Mr Liu picked up his car, and seized tapes from the closed-circuit television system. Mr Liu, who lived in the estate with his family, ran an engineering company which was involved in government projects.