Four men are being sought over the remote-controlled projectile-launching device found buried in the Happy Valley racetrack last week. Police made the announcement yesterday as a HK$1 million reward was posted by the Jockey Club for information leading to their arrests. Police gave a detailed description of the device, which was buried at the starting point for the first race of last Wednesday's night meeting. It consisted of a 12-metre hose connected to an electrical device, a compressed gas cylinder and a camera lens. 'Twelve sets of two to three metal tubes were connected to the polythene hose through sets of valves at regular intervals,' a statement said. Nails and an unidentified solution found inside some of the tubes were being examined at the government laboratory, a source said. The device 'could have resulted in serious injuries to horses or persons', the statement said. Police said the four men being sought had been seen at the track's 1,200-metre starting point two days before the race meeting, and again very early last Wednesday. The second time they were spotted was hours before the device was discovered by Jockey Club track supervisor Jackson Wong Chak-shuen. Officers said the men were aged between 25 and 40. 'No sketches of the four men can be drawn because of limited information,' a police source said. 'We hope a high reward can turn up information that will help solve the case.' A Jockey Club spokeswoman said the reward 'demonstrates how seriously we are taking the case'. The club has stepped up security measures at the Sha Tin and Happy Valley racecourses since the incident. Police have set up a telephone hotline (2548 2657) and an e-mail account address, email@example.com for leads on the case. Information can also be passed on in writing to General Post Office Box No 999 or the Crime Information Faxline on 2520 2828.