How would the criminal justice system be different today if the founding fathers had decided not to create a separate system of federal courts?

If there were no separate system of Federal Courts for enforcing the law and justice in the national level, the extent of applying criminal justice system would have confined to the extent of state level.
A higher authority is necessary to look after some of the major issues not discharged by the state courts. The cases are divided among these two courts according to some criteria’s such as how severe a case is and magnitude of the case.