Tony Kenway, 39, was found dead in a red Porsche Cayenne GTS in front of the Sanit Sports Club in Tambon Pong at 10.30am and police investigators initially suspected that he may have been killed because of a business dispute or personal conflict.
Provincial Police Region 2 chief Pol Lt-General Jitti Rodbangyang said the case was a serious crime that affected public morale and could affect tourism because the victim was a foreigner.
He instructed officers to inspect security cameras along possible escape routes used by the shooter and his getaway driver, as well as interview witnesses and gather evidence to bring the culprits to justice.
Police would also notify the British Embassy, he said.