In which scenario would the concept of "res judicata" apply?

Res judicata, also known as claim preclusion, is a legal doctrine that prevents parties from relitigating issues that have already been resolved in a final judgment by a competent court. This principle is rooted in the need for judicial economy and the finality of decisions, ensuring that once a dispute has been settled, it cannot be reopened simply because one party is dissatisfied with the outcome.

In the context of the scenario mentioned, when a case has already been decided on its merits and the judgment is final, the doctrine of res judicata applies. This means that the issues addressed in that case cannot be litigated again in any future lawsuits involving the same parties or their privies. The underlying rationale is to provide closure to disputes and to uphold the integrity of judicial decisions.

Other scenarios, such as needing a new trial due to new evidence, a defendant changing their plea, or a witness failing to appear, do not involve a final judgment on the merits that would invoke the principles of res judicata. Instead, these situations relate to procedural aspects of the case and do not affect the finality of a prior judgment.