According to Nolo.com: "In 1998, Congress passed the Identity Theft and Assumption Deterrence Act. (18 U.S.C. § 1028).
The Act makes the use of another person's identification with the intent to commit any unlawful activity a federal felony. Federal agencies- including the U.S. Secret Service, the FBI, and the U.S. Postal Inspection Service- investigate suspected violations of the Act. The U.S. Department of Justice handles prosecutions.
Federal law enforcement agencies usually do not investigate individual cases unless the dollar amount is high, or the victim is one of many people victimized by the same perpetrator or fraud ring. Additionally, many states have passed or are considering laws related to identity theft."