Police said that according to witnesses, Pol Sr Sgt Maj Ekapong Sakdayuth, 65, was attacked at his petrol station about 6.50am.
Two men arrived on a motorcycle, idicating they wanted to buy fuel. Then they opened fire at him.
When Ekapong fell to the ground, they poured petrol on his body and set him on fire.
The two then walked into the office and took a notebook computer, cash and a bag containing documents before fleeing.
Police were investigating.