Story highlights Fake prescription painkillers are the suspected cause of an overdose cluster in Georgia this week

One of the drugs in the pills is still a mystery and may be a new compound

(CNN) Two synthetic opioids have been found in fake prescription pills suspected to have caused a cluster of overdoses this week in Georgia, including four deaths, according to a statement from the Georgia Bureau of Investigation.

One of the drugs is still unidentified and may be a new compound, according to a GBI representative.

"The fact that the GBI Crime Lab has never seen it is a very bold statement," said Nelly Miles, director of the GBI Office of Public Affairs and a forensic chemist by training. "We're essentially working it up from scratch."

The unknown opioid is a modified type of fentanyl that the GBI Crime Lab had never seen, the bureau said. The pills were made to resemble the prescription painkiller Percocet and sold on the street, according to state officials.

Miles said synthetic drugs like this one are coming in from overseas, where fentanyl molecules are altered slightly in an effort to skirt US laws. Then, they may be packed into pill presses in the United States, she said.