Investigators have agreed to hear from nine more proposed defence witnesses in the money laundering case against Panthongtae "Oak" Shinawatra, but say the process must be completed by March 15 to avoid any further delay.
Mr Panthongtae, son of former prime minister Thaksin, has made repeated calls for "justice" since he and three others were charged with alleged involvement in relation to the approval of large unsecured loans for a blacklisted client of the Krungthai Bank (KTB) during the Thaksin administration.
Mr Panthongtae's lawyer earlier asked the Department of Special Investigation to interview 21 more witnesses, but investigators selected only eight who were directly linked with case.
Last month the suspect continued what were seen as delaying tactics, asking the officers to add three more suspects.
"We resolved to question nine more witnesses," Kajornsak Buddhanuparb, chief of the Office of Attorney-General's Department of Investigation 3 said on Wednesday after meeting with DSI investigators.
If they do not report to investigators by March 15, their right to testify will be revoked, Mr Kajornsak said.
The witnesses' repeated postponement of meeting dates has annoyed investigators, who view it as a deliberate delaying tactic with the statute of limitations in the case due to expire in December this year and the investigation still to go through a lengthy process.
After March 15, the investigators will be occupied wrapping up the case report before forwarding it to prosecutors, Mr Kajornsak said. The prosecutors will then decide whether more witness accounts are needed before indictment.
The eight defence witnesses were called to testify between Jan 16 and 14, but failed to turn up. They instead put back the interrogation to early February, and eventually, Mr Kajornsak said, only six met with the DSI.
He said the investigators have allowed Mr Panthongtae his legal right to request more witnesses be allowed to testify on his behalf, but he too must "respect the investigators' right" to complete the case within the set time frame.
Frequent petitions for justice was a frequent tactic used by well-to-do people to buy time, he said.
On Jan 25, Mr Panthongtae's lawyer Chumsai Sriyaphai also called for justice, petitioning Justice Minister Prajin Juntong over alleged interference in the case.
The four suspects were accused of laundering money after receiving cheques worth 10 million baht and 26 million baht connected with the dubious KTB loans.
The bank granted 9.9-billion-baht in loans to subsidiaries of the Krisdamahanakorn real estate company even though the company was listed with the bank as a non-performing debtor.