The doctrine of issue estoppel in criminal matters

The doctrine of issue estoppel in criminal matters applies when a competent court has previously resolved a factual issue in favor of the accused. Once such a finding has been made, it serves as an estoppel or res judicata against the prosecution, preventing the introduction of evidence to challenge that finding in subsequent trials, even if those trials involve different offenses. However, it does not bar the prosecution from trying or convicting the accused for a separate and distinct offense.

For the doctrine of issue estoppel to apply, the parties in both trials must be the same, and the fact in issue that was determined in the initial trial must be identical to the fact in question in the subsequent trial. Issue estoppel differs from the autrefois principle: while autrefois bars the prosecution from challenging the entire verdict, issue estoppel prevents the re-litigation of specific factual issues that have been decided. The Criminal Procedure Act and Evidence Act of 1967 in Tanzania do not explicitly include the doctrine of issue estoppel. Instead, sections 137 and 280 of the Criminal Procedure Act embody the autrefois principle, and section 123 of the Evidence Act embodies estoppel by declaration, act, or omission.

The purposes of the doctrine of issue estoppel are to ensure:

1. Fairness to the accused, who should not be required to address issues previously resolved in their favor;
2. The integrity and coherence of criminal law; and
3. The respect for judicial findings and the efficient use of judicial resources.