The Assimilative Crimes Act (18 U.S.C. § 13) is the law that allows the federal government to use state law to prosecute offenses committed on federal government land or in federally owned buildings.
When a criminal offense has been committed on land or buildings that have been reserved or acquired by the federal government, and the offense is not defined under federal law, state law will apply to the offense under the Assimilative Crimes Act. When the federal government decides to prosecute the offense – through the U.S. Attorney’s office - it is not enforcing the state law. It is enforcing federal law and order by applying the state law to the offense.
State law is applied under the Assimilative Crimes Act only when the U.S. Congress has not enacted a statute that prohibits a criminal offense. For example, generally there is no federal crime of murder, but each state, including Mississippi, has enacted laws providing the legal elements of murder, manslaughter, etc. If you were to kill someone on federal land in Mississippi, you would likely be prosecuted in federal court, but that court would apply, or “incorporate,” Mississippi’s definition of murder. The federal court would require the prosecutors to prove all of the elements of your charged offenses according to Mississippi law.
Under the ACA, the federal government may not apply state regulatory laws to a criminal offense. Also, the federal government may not incorporate state administrative penalties to a criminal offense, such as the suspension of a driver’s license or any other state license. When a federal court applies state substantive law, and possibly federal procedural law and the federal sentencing framework, it can make even the most mundane criminal matter complex and confusing. It is not a place to be without competent advice. If you find yourself in federal court charged with an offense defined by state law, give us a call.