POLICE have warned the staff of all betting shops to be on alert tomorrow following Wednesday's attempted bombing. They fear the man responsible holds such a strong grudge against the Royal Hong Kong Jockey Club that he may strike again during race day at Sha Tin. An analysis of the bomb parts by forensic law scientists and of the tape of the man telephoning his warning has yielded no clues. The police acknowledge that their best chances of catching the man would be if he tries to repeat the extortion demand. A police source said yesterday that the bomb was made of parts which were easily obtainable. The man had not explained what his problem was other than that he was a disgruntled punter, which made it impossible to piece together a profile of him. The highly-sophisticated bomb was left in a Tai Wai off-course betting centre on Wednesday night. A man telephoned the Jockey Club to say he had planted it and would turn up later to pick up an unspecified sum of money. However, staff at the Jockey Club discovered the device before he arrived and it was defused by a bomb disposal officer. The man responsible never turned up to claim any cash.