The other suspect is Yong Dodkhruea.
The Criminal Court on the same day ordered the duo to testify before the court next Monday.
CCD investigators then wrapped up and forwarded the case to prosecutors at the Department of Corruption Litigation on March 30.
Mr Premchai, the 63-year-old president of the Italian-Thai Development Plc, Mr Yong, 65, and two other individuals were arrested on the night of Feb 4 for allegedly engaging in illegal hunting activities in the sanctuary, which is a Unesco World Heritage site.
The other two are Nathee Riamsaen and Thanee Thummat.
They were found in possession of several dead animals, including a rare black leopard and its pelt. Mr Premchai insisted he did not shoot the leopard and maintains his innocence.
The tycoon alone initially faced six charges: carrying firearms in public without permission, colluding to hunt wildlife in a wildlife sanctuary without permission, conspiring to hunt protected wildlife without permission, possessing protected wildlife carcasses without permission, concealing wildlife carcasses obtained illegally, and collecting wildlife items in a national forest reserve without permission.
The tycoon on Tuesday (May 22) also pleaded not guilty in the Criminal Court to another charge concerning illegal possession of firearms after 43 firearms were found during a Feb 7 search of his home.
The Kanchanaburi Provincial Court on Monday (May 21) rescheduled an examination of evidence and witness lists in the illegal hunting case against the four until June 6 at the request of two defendants.
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