What must happen for a defendant's confession to be admissible if there's a co-defendant?

For a defendant's confession to be admissible when there is a co-defendant involved, it is crucial that the confession does not infringe upon the co-defendant's right to confront witnesses. The Confrontation Clause of the Sixth Amendment provides that a defendant has the right to confront those who are against them in a criminal trial, which includes being able to cross-examine witnesses or evidence presented by the prosecution.

When a confession implicates a co-defendant, there can be significant issues related to fairness and the right to confront witnesses. If the confession is admitted in a way that violates this right, it can lead to a reversal of a conviction or a violation of due process. For example, if a confession includes statements against the co-defendant that they cannot cross-examine, this could be considered prejudicial to the co-defendant's case.

The other options, while they may include elements that could be important in certain contexts, do not directly address the critical issue of the co-defendant's right of confrontation. Therefore, ensuring that the confession's presentation does not impact these rights is essential for the confession's admissibility.