A U.S. citizen was one of four suspects arrested in a series of coordinated raids in Costa Rica on Tuesday to dismantle a criminal group that stole thousands of dollars from credit and debit card holders by cloning their cards, according to the Judicial Investigative Police (OIJ).

According to an investigation, the suspects used devices known as “skimmers” to steal card data from unsuspecting victims.

The devices do their work after a criminal inserts the thin plastic device into an ATM machine’s card reader.  The device than reads and stores every ATM users’ card information the moment they insert the card into the machine.  The criminal returns later in the day and retrieves the device, which may by then have the full data of hundreds of cards stored on it. That information is later used to create clones of the users’ cards, or for online purchases.

The skimmers are also sometimes placed in the credit card terminals at retail establishments, restaurants, and other places that accept credit cards.

As of Tuesday morning, authorities said that the group is believed to have stolen some US $150,000, though that figure could increase as the investigation continues.

Most of the purchases made with the cloned cards occurred in the United States, and officials said some of the victims are also believed to be located abroad.

Officials said that the leader of the group was a Costa Rican employed by the Costa Rican Electricity Institute (ICE).

Authorities were able to confiscate skimming devices as well as electronic equipment used for card cloning during the raids in Escazu, Guadalupe, San Isidro de Alajuela and San Francisco de Dos Rios.