The driver of the tour bus that crashed on Wednesday night killing 18 was high on Ya Ba or amphetamines.
Police have dismissed his suggestion that the brakes failed as they saw skid marks on the road surface.
Kritsana, 45, initially fled the scene of the accident on a hill in Wang Nam Khiaw district but was soon arrested.
His blood was free of alcohol but there was Ya Ba traces in his urine. He admitted taking the stimulant before leaving Chantaburi.
Kritsana, from Kalasin, said the brakes failed but investigators doubt that due to the evidence.
Confusion surrounds his status to be driving at all.
It was reported that he had a Type 2 license valid until 2019 but his driving license was out of date.
Pol Lt Gen Damrongsak Kittipraphat said on Facebook that the driver was detained at Udomsap police station.
Police said they suspected that he was going too fast probably influenced by the Ya Ba in his system and was not familiar with the road.
Times comment:-Once again a terrible accident has occurred because of a driver who did not even have a valid driving licence. Only one question comes to mind,”How can this possibly happen?”
(Source:-Sanook