"This group was considered to be a big network that spanned many countries," including Thailand, Myanmar, Singapore, Malaysia, Indonesia, Taiwan, Hong Kong and the Philippines, Somyot said.
According to Thai police, Hunter served in the U.S. Navy, and his alleged accomplices were also believed to have had military training.
"All these people were trained to kill," Somyot told reporters Thursday at a police airport in Bangkok after the handcuffed suspects were flown in from Phuket.
He said the DEA contacted Thai authorities several months ago to say that Hunter was believed to be hiding in Phuket, where he had rented a house. Hunter regularly traveled around the region and last entered Thailand from the Philippines on Sept. 6, Somyot said.
U.S. Embassy spokesman Walter Braunohler in Bangkok said he could not immediately comment on the case and referred questions to Washington.