Do you understand the difference between a state crime and a federal crime? Most crimes are state crimes which are investigated and prosecuted by state and local officials. For example, murder, rape, robbery, shoplifting, and most other thefts are typical state offenses which would go through your state trial courts and be prosecuted by a state district attorney. Typically, federal crimes, on the other hand, are a narrower classification of crimes that have been carved out by Congress as federal offenses due to some perceived federal nexus or interest. The most common way to tell the difference is whether or not the crime has an interstate connection. For example, as to kidnapping, Congress has made it a federal offense if the victim is transported in interstate commerce, i.e. across a state boundary. (On the other hand, if the kidnap victim is not taken across state lines, it would remain a state crime and be prosecuted by a state prosecutor). As to thefts, where it is prosecuted will generally depend upon whether or not the accused has transported the stolen automobiles or other merchandise across state lines.
Bank robbery is another example of a crime carved out by Congress as a federal offense, because most bank deposits are federally insured.
In many cases, a crime may be in violation of both federal and state law. For example, many drug cases implicate both state and federal law. (This is called concurrent jurisdiction and will be addressed more fully in a later blog article). In such cases, generally, the more serious drug cases with interstate connections will be prosecuted in federal court. As a former federal prosecutor, I would often contact my state counterpart and we would decide together which one of us should take the case.
So, the bottom line is: if you want to avoid being prosecuted in federal court, then you had better avoid crossing the state line! And even then, you had also better hope you haven't committed an offense in which Congress has found a federal interest!