LEWISTON – Authorities are investigating counterfeit money that showed up at area businesses over the past month.

Lewiston police and Secret Service agents are heading up the search for the source of the bogus bills, handed out in denominations of 10s, 20s, 50s and 100s, police Lt. Michael McGonagle said.

The first call came the end of May from Victor News, a variety store on Park Street, McGonagle said. Local police immediately called in the Secret Service. Since then, at least a dozen other stores in Androscoggin County have contacted authorities, he said.

Other stores in Maine have spotted phony bills, too, but Central Maine appears to be one of the regions where they’re concentrated, authorities said.

The bad bills are typically mixed in with the real thing during transactions and taken by busy cashiers, McGonagle said. Later in the day, when the till is emptied and counted, the bills are flagged as suspicious. Banks taking deposits from stores also are noticing the bad bills.

Authorities have narrowed their search to “people of interest,” aided by surveillance cameras at some of the stores, police Detective Lee Jones said.

Although counterfeit money is always in circulation, batches of it show up in stores in waves, Jones said. “In the past year, there’s definitely been an increase,” he said.

Advances in technology, computer printers and copiers make better and better facsimiles of the real thing, McGonagle said.