Which amendment relates to the voluntariness of a confession?

The amendment that relates to the voluntariness of a confession is the 14th Amendment. This constitutional provision includes the Due Process Clause, which ensures that no person shall be deprived of life, liberty, or property, without due process of law. In the context of confessions, the Supreme Court has ruled that confessions must be voluntary to be admissible in court. A confession that is obtained under coercion, duress, or improper influence would violate an individual's due process rights under the 14th Amendment.

Cases such as Miranda v. Arizona emphasize the importance of ensuring that individuals are aware of their rights and that their confessions are given freely and voluntarily. Therefore, the 14th Amendment directly addresses the circumstances under which confessions can be deemed acceptable in the legal system, focusing on the necessity of voluntariness to uphold the principles of justice and fairness.