The certificate of any forensic scientist employed by the Commonwealth on behalf of the Board or the Department of Forensic Science, when signed by him, shall be evidence in all prosecutions for violations of this subtitle and all controversies in any judicial proceedings touching the mixture analyzed by him. On motion of the accused or any party in interest, the court may require the forensic scientist making the analysis to appear as a witness and be subject to cross-examination, provided such motion is made within a reasonable time prior to the day on which the case is set for trial.
Va. Code § 4.1-352