Where the combined effect of individual harmless errors renders a criminal defense “far less persuasive than it might [otherwise] have been,” the resulting conviction violates due process. (Chambers v. Mississippi (1973) 410 U.S. 284, 294, 302-303.) Parle was convicted of first degree murder for the killing of his wife. The only issue in dispute was Parle’s state of mind, Parle’s defense being that, at most, the killing was second degree. At trial, the court improperly admitted damaging testimony from Parle’s psychiatrist but excluded evidence of an expert psychiatric witness and admitted evidence of Parle’s threat to a peace officer five years prior but excluded evidence of his wife’s verbalized threats against Parle a few days before the killing. The California Court of Appeal agreed that there were numerous and serious errors but upheld the conviction, concluding that the errors, both individually and collectively, were harmless because the included/excluded evidence was essentially cumulative and it was not probable a different verdict would have occurred but for the errors. The Court of Appeals observed that the improperly admitted evidence bolstered the theory offered by the prosecution whereas Parle’s defense was rendered less persuasive as a result of evidence being erroneously excluded. As a result of this denial of due process, it affirmed the district court’s granting of Parle’s habeas petition, noting that although the California Court of Appeal’s decision identified the correct governing legal principle, it unreasonably applied it to the facts of the case.