PHILADELPHIA (CBS) — Philadelphia police have arrested five Liberian men accused of running a phony moneymaking swindle.

Investigators say undercover cops conned the men after getting a tip from a West Philadelphia business owner who had been approached by the five Liberians with an alleged offer to trade $50,000 for $100,000 in so-called “black currency.”

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Police spokesman Ray Evers says the scammers attempt to convince the victim that the US currency has been smuggled into the country by soaking it in black ink.

“They’ll cut open a large stack of US currency that’s painted black. They’ll pull the top two dark bills out. Money is placed in some tin foil, and they use a special compound liquid to extract the dark ink from the US currency,” said Evers, describing the phony “recovery” procedure.

It looks legitimate, Evers says, until the victim goes home and finds he has nothing but a stack of black paper.

Evers says the ruse was revealed in a sting operation on November 18 at a store in the 7500 block of Haverford Avenue.

The five men arrested were identified (top to bottom) as:

Nagbe Saykagee, 30, of the 200 block of Sanford Road, Upper Darby

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Patrick Sanyeah, 27, of the 4600 block of Chester Avenue, Philadelphia

Solomon Bility, 26, of the 300 block of East 24th Street, Chester

Rovia Dousuah, 24, of the 100 block of North Front Street, Darby, and

Isaac Johnson, 36, of the 2500 block of South Ashford Street, Philadelphia.

The suspects are being prosecuted by local authorities, but the US Secret Service has taken an interest in the case. And police are repeating the age-old warning to business owners: if it looks too good to be true, it probably is.

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Reported by Paul Kurtz, KYW Newsradio 1060.