Widely known by the nickname "Jo Ferrari", Pol Col Thitisan Utthanaphon accused of torturing and killing a drug suspect while in custody handled cases involving 368 smuggled cars during 2011-17.
Patchara Anuntasilpa, the department's director-general, said the department examined its records and found that Pol Col Thitisan had been the official in charge of confiscating 368 illegally imported vehicles, including luxury cars and supercars, during the period.
Of the total, 363 cars were auctioned, raking in about 1 billion baht, and the remaining five have not been sold.
According to customs regulations at the time, 30% of the proceeds from all smuggled products were incentives for police teams or those bringing cases to the attention of authorities and 25% were rewards to other officials, including police.
He said Pol Col Thitisan was among the beneficiaries of the rules but declined to disclose information about the recipients. The data would have to be first forwarded to authorities concerned, he added.
Mr Patchara pointed out the regulations were repealed in 2017 and the incentive and reward rates have since been changed to 20% each and capped at 5 million baht total per case.
The customs chief also admitted he had heard rumours that his department's auctions of smuggled cars had attracted little interest because they were believed to have been dominated by a group of bidders with an advantage. He declined to confirm or deny them.
According to the rumours, the electronic control units of the vehicles had been removed before they were sent to the Customs Department and only people with access to the units could use them. This means winners outside this group had to pay extra for them.
The department's explanations followed media reports that police had found 13 luxury cars worth more than 100 million baht in total at Pol Col Thitisan's 60-million-baht house.
His wealth also prompted the National Anti-Corruption Commission (NACC) to step in. As a police colonel, he received a salary of around 40,000 baht a month before he was dismissed from service on Tuesday.
Niwatchai Kasemmongkol, NACC spokesman, said his office was investigating Pol Col Thitisan for abuse of authority and unusual wealth. Anti-graft officials are gathering facts for the investigations.
However, he noted that the abuse of authority probe over torture of the drug suspect is being sought by the anti-graft agency's Region 6 and the NACC has yet to determine if the case falls under its jurisdiction.
A source in the NACC said allegations of bribe-taking and use of nominees in holding assets worth over 200 million baht will also be forwarded to the NACC’s subcommittee on assets inspection for consideration.
One of his estranged actress girlfriends told Thai media in 2017 that he had offered to give her 230 million baht in cash held by a nominee.
Srisuwan Janya, secretary-general of the Association for the Protection of the Thai Constitution, on Thursday submitted a petition to the Public Sector Anti-Corruption Commission (PACC) to investigate Pol Col Thitisan and six others.
The 39-year-old and six other police were accused of torture and killing of a drug suspect earlier this month while trying to extort 2 million baht from the suspect.