The National Anti-Corruption Commission (NACC) said it has found no evidence implicating Industry Minister Suriya Jungrungreangkit in a dereliction of duty case.
It was referring to a case linked to the purchase of 10 ultra-long-range aircraft between 2002 and 2004, believed to have plunged Thai Airways International Plc (THAI) into debt.
However, this does not mean Mr Suriya was not involved at all in the case and he could still be charged if new evidence emerges to convince the NACC that he was at fault, said Niwatchai Kasemmongkol, secretary-general of the NACC.
Mr Niwatchai was responding to reports suggesting Mr Suriya is innocent.
At this point, the NACC believes Mr Suriya was not involved in THAI's purchase of the 10 aircraft, he said.
The NACC in December resolved to press charges of dereliction of duty against ousted prime minister Thaksin Shinawatra, former deputy transport minister Phichet Sathirachawal, former THAI board chairman Thanong Bidaya and former THAI president Kanok Abhiradee, while Mr Suriya, who was initially included in the investigation, was not charged.
The NACC sent a letter to the four parties asking them to explain the charges against them, Mr Niwatchai said.
For Thaksin, who is living in self-imposed exile abroad, the letter was sent to his address in Thailand. In the event Thaksin fails to respond, the NACC will assume he has forfeited his right to defend himself in this case.
Between 2002 and 2004, Thaksin's cabinet approved THAI's plan to purchase 10 A340-500 and A340-600 aircraft worth about 53.5 billion baht.
The purchase plan was submitted by Mr Suriya, according to a report by Isra News Agency.
On Aug 28, 2020, former deputy transport minister Thaworn Senneam disclosed findings from an investigation into alleged mismanagement and corruption at THAI.
He said the purchase of the 10 Airbus craft was the beginning of the national flag carrier's plunge into debt, which has resulted in it requiring financial rehabilitation up until now.
The aircraft were in service between July 2005 and Jan 7, 2013, on 51 routes, including Bangkok-New York and Bangkok-Los Angeles. But THAI ended up suffering 39.8 billion baht in total losses on all the routes, he said.
In particular, flights on the Bangkok-New York and Bangkok-Los Angeles routes recorded losses of more than 12.4 billion baht, he said.
The aircraft were in use for only six to 10 years, lower than the general threshold of 20 years of service, which was not cost-effective, Mr Niwatchai said.
In total, THAI lost at least 62.8 billion baht as a result of this aircraft procurement plan, he added.
Mr Phichet, meanwhile, said Mr Suriya had given him some advice over the phone recently, saying it is the responsibility of THAI's board to decide any aircraft purchasing plan before submitting it to the cabinet via the Ministry of Transport.
In an interview with Isra News Agency, Mr Phichet said that even though he was responsible for supervising THAI's operations, the authority to forward the plan lay with the transport minister.