Public prosecutors indicted construction magnate Premchai Karnasuta and his associate on a charge of bribery Wednesday in connection with their alleged poaching in Kanchanaburi's Thungyai Naresuan wildlife sanctuary in February.
The other suspect is Yong Dodkhruea.
The Criminal Court on the same day ordered the duo to testify before the court next Monday.
The move came after Wichian Chinnawong, the wildlife sanctuary chief who led a team to arrest Mr Premchai, lodged a petition with the Counter-Corruption Division (CCD) on Feb 8, urging the agency to pursue legal action against the tycoon and Mr Yong on a charge of colluding in bribing authorities which breaches the Criminal Code.
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.
They are 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 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 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.
