Elderly U.S. residents were the target of a $10 million “sweepstakes scheme” for which a U.S. resident living in Costa Rica pleaded guilty Feb. 2, the Justice Department said.

Kristian Francis Sierp, 45, formerly of Boca Raton, FL, pleaded guilty to one count of conspiracy to commit mail and wire fraud, one count of mail fraud and one count of conspiracy to commit money laundering. As part of his plea, he admitted that from approximately January 2011 through September 2015, he worked in various illegal Costa Rican call centers belonging to co-conspirator Elliot Rosenberg, where they placed telephone calls to U.S. residents, falsely informing them that they had won a substantial cash prize in a contest.

The victims were told that to receive the prize, they had to pay a purported “refundable insurance fee,” Sierp said. After he received victims’ money for an initial fee, he said, he would contact the victims again to demand additional purported fees to cover even larger promised prizes.

Sierp said that he and his co-conspirators continued their attempts to collect additional money from a victim until that victim either ran out of money or discovered the fraudulent nature of the scheme, according to the Justice Department. To further their fraud and mask that they were calling from Costa Rica, Sierp and his co-conspirators often falsely claimed that they were calling on behalf of a U.S. federal agency and used voice over internet protocol phones that displayed a 202 area code, giving the false impression that they were calling from Washington, D.C., he said.

Sierp also pleaded guilty for his role in a $2.5 million high-yield investment fraud scheme.