When the legislature of the Untied States passes a law that makes a certain act illegal the crime is a federal offense. These laws govern more serious crimes such as kidnapping, fraud and drug charges.
When a crime crosses state lines or uses a federal service (such as sending drugs by mail or use of fraudulent social security benefits) the crime is considered a federal matter. If you rob a bank or a post office, that can also be a federal offense.
If you are prosecuted by the federal government for a crime, you may also be prosecuted for the same crime in a state court.
Posted in: Federal Offenses