In Stanton v. Superior Court (1987) 193 Cal.App.3d 265, the prosecutor failed to turn over to defense counsel an investigative report, received before the preliminary hearing, that included three key witnesses' statements taken shortly after the accident that cast doubt on the credibility of their later preliminary hearing testimony regarding the circumstances of the vehicle accident they had observed. (193 Cal.App.3d at p. 268.) The Court of Appeal held that the defendant was entitled to have the investigative report before the preliminary hearing because it "contained exculpatory evidence on the focal issue before the magistrate and would have served the dual purpose of impeaching the prosecution's case and establishing an affirmative defense to the gross negligence" allegation of the vehicular manslaughter charge. (Id. at p. 272.) The Court of Appeal held that "Nondisclosure of evidence impeaching eyewitnesses on material issues is the deprivation of a substantial right," and "The magistrate, having heard the impeachment of the three key witnesses, might well have stricken the gross negligence allegation . . . ." (Ibid.)