A subpoena requiring the attendance of a witness at a trial or hearing conducted under this article may be served at any place in the Commonwealth. A civil action under § 8.01-216.4 or 8.01-216.5 may not be brought (i) more than six years after the date on which the violation is committed or (ii) more than three years after the date when facts material to the right of action are known or reasonably should have been known by the official of the Commonwealth charged with responsibility to act in the circumstances, but in that event no more than ten years after the date on which the violation is committed, whichever occurs last. If the Commonwealth elects to intervene and proceed with an action brought under § 8.01-216.5, the Commonwealth may file its own complaint or amend the complaint of a person who has brought an action under § 8.01-216.5 to clarify or add detail to any claim in which the Commonwealth is intervening and to add any additional claim for which the Commonwealth contends it is entitled to relief. Any complaint filed by the Commonwealth pursuant to this paragraph shall relate back to the filing date of the complaint of the person who originally brought the action, to the extent that the claim of the Commonwealth arises out of the conduct, transactions, or occurrences set forth, or attempted to be set forth, in such person’s complaint. In any action brought under § 8.01-216.4 or 8.01-216.5, the Commonwealth shall be required to prove all essential elements of the cause of action, including damages, by a preponderance of the evidence. Notwithstanding any other provision of law, a final judgment rendered in favor of the Commonwealth in any criminal proceeding charging fraud or false statements, whether upon a verdict after trial or upon a plea of guilty or nolo contendere, shall estop the defendant from denying the essential elements of the offense in any action that involves the same transaction as in the criminal proceeding and which is brought under § 8.01-216.4 or 8.01-216.5.