By The Nation
There were no witnesses to the incident.
Pol Senior Sgt Maj Phadet Phulonkaew, 47, who was last seen following a truck, suffered a broken neck and severe chest injuries.
Police suspect that the truck might have suddenly stopped for some reason and the policeman's motorcycle crashed into the rear of the truck.
The officer's body and his damaged motorcycle were found later.
Police said they will check security camera footage on the expressway to try to locate the truck.
Phadet was on duty from midnight to 6am.