The family of Phattharachai Atthaporn, 68, is suing the HPD and the rescuers for their part in the oversight, reports the Bangkok Post.
Mr Phattharachai was driving along a motorway heading to Pattaya on Aug 9 when his vehicle veered off the road and crashed.
When police and rescuers arrived and approached the mangled wreckage they failed to notice whether Mr Phattharachai was still in the vehicle.
The car was towed to the police station with the victim still inside and left there for 12 hours before the police returned and discovered the body.
The HPD and the rescuers came under heavy fire for their alleged negligence, prompting the division to hold a joint press conference with the Highways Department to explain the matter on Friday (Aug 12).
HPD Commander Pol Maj Gen Ekkarat Limsangkan offered his regret over the incident and said a fact-finding panel has been set up jointly with the Highways Department to investigate the oversight.
He said officers initially did not see the driver and thought he may already have been taken to hospital. It was not until investigators found no hospital had admitted Mr Phattharachai that they returned to the wrecked car and discovered his body inside.
Mr Phattharachai’s family indicated earlier that if he had been taken to hospital promptly he might have survived.
Dr Pakorn Wasinrat, from the Institute of Forensic Medicine, said the man suffered serious injuries which may have caused death minutes after the crash.