Freedom from double jeopardy guaranteed by?

Answer 1

As a matter of constitutional law, at the federal level the 5th Amendment to the US Constitution. At the State level, the 14th Amendment due process clause that "passes through" the 5th Amendment individual protections as restrictions on State governments.

Many state constitutions expressly incorporate the right; every state has some rules of criminal and court procedure, as well as case law, that define the procedural steps and safeguards.