The 400-rai expo site in Muang district's Tambon Mae Hia that was said to belong to the Agriculture Department was actually part of Doi Suthep National Park, said Veera Somkwamkid, secretary-general of the People's Network against Corruption.

"It's suspicious how the previous administration could approve such a thing and even give it Bt2.6 billion in funding," he said.

Kasetsart University was hired as the event's adviser and designer but it then hired a company to do the work and to avoid being caught for breach of contract, changed the project's name, he said.

Anan Dalodom, president of the Horticultural Science Society of Thailand, said many of the project contractors had cross-shareholdings. Reed Tradex Co was hired for Bt369 million to coordinate the event but the department was stuck paying Bt31 million more due to the company's incapability, he said.

CKNNL Co quoted a price very close to the government's median price after the government had lowered the prices for six construction materials, Anan said, adding that the contractor-hiring approvals were made in a very short time and not given thorough consideration.