"One of our officers developed some information on a counterfeiting ring being operated over in Antioch," he said. "Our guys went over there and discovered a counterfeit ring."
Oakley police officers, along with Secret Service agents, took four people into custody in the early morning hours at a Ramada Inn in Antioch, Thorsen said. Officers found computer equipment, printers and bills in the room.
"It appears they were converting lower-denomination bills, like ones, into hundreds," Thorsen said.
It is not yet clear whether the four suspects will face state or federal charges, he said.
Police are continuing to investigate the operation and do not know how much fake money the group has passed, Thorsen said.