(CBS News) Federal investigators have raided a diplomatic compound just outside of Washington, D.C. They’re looking into allegations of human trafficking on the property. But investigators already face a huge legal hurdle: diplomatic immunity.

After a tip to a telephone hotline, agents from the State Department spoke to two Filipino women employed in a compound owned by the Saudi military in McLean, Va., just across the Potomac River from Washington.

The women told agents they are household workers brought to the U.S. legally, but they complained they’ve never been allowed to leave the compound and said they felt like indentured servants. Special agent John Torres, of the Department of Homeland Security, calls it a possible case of human trafficking.

He said, “The women are safe, and they are being interviewed by a number of different people, including our agents and our victim witness coordinators.”

Cases like this, in which foreign workers complain of being virtual slaves to foreign diplomats in America, are not uncommon. Advocates for the victims say the State Department and Homeland Security are investigating more cases than ever. The problem is diplomatic immunity.

Martina Vandenberg, of the Human Trafficking Pro Bono Legal Center, said, “It’s very difficult to prosecute someone with full diplomatic immunity.”

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