Although precedent establishes no bright line rule that an expert witness for the defense is needed in every sexual assault case, here, the habeas court had ample evidence from which it could conclude that trial counsel should have presented expert testimony on the reliability of a disclosure of sexual abuse by a developmentally delayed child, elicited after multiple interviews conducted in an accusatory context, and that by failing to do so, counsel's performance was deficient. After a four year old child with whom he lived was found infected with trichomonas and eventually made statements about him, Michael T. was convicted of sexual assault in the first degree and risk of injury to a child. His petition for a writ of habeas corpus was granted and the Appellate Court affirmed the judgment. The Supreme Court reversed the judgment insofar as it rested on a finding that the petitioner's trial counsel failed to challenge effectively the state's inculpatory medical evidence. The Supreme Court found that counsel, by means of cross-examination of the state's experts and his closing argument, established that trichomonas could be contracted through nonsexual means and no prejudice resulted from the lack of a defense expert on the issue. The Supreme Court remanded the matter for the Appellate Court to determine whether counsel's failure to present expert evidence to challenge the state's expert on psychological issues relating to the child victim's credibility constituted deficient representation. Finding that the habeas court properly determined that counsel's failure to utilize such an expert at trial constituted deficient performance, the Appellate Court affirmed the habeas court's judgment on this ground. The respondent commissioner of correction's assertion was rejected that counsel's cross-examination of the state's witnesses sufficiently informed the jury about the psychological issues. Counsel failed to elicit any information regarding the psychological issues related to the child's disclosure of sexual abuse raised by the petitioner's expert during the habeas trial, including the effects of an accusatory atmosphere, repeated questioning and possibility of a rehearsal effect, the child's developmental delay and problems associated with the forensic interview. Based on the evidence, there was a reasonable probability that the outcome of trial would have been different if such testimony had been presented to the jury.