The right to due process guaranteed by the Fifth and Fourteenth Amendments prohibits the exclusion of probative exculpatory evidence in criminal trials when exclusion of such evidence is unreasonable, arbitrary, or disproportionate.

The stated rule is extremely vague. But no more precise statement of the rule is possible because the Supreme Court has refused to state the rule in more precise or different terms. But in particular factual settings the few Supreme Court decisions involving similar situations may provide some guidance.