Section 72A. If a person commits an offense or violation prior to his eighteenth birthday, and is not apprehended until after his nineteenth birthday, the court, after a hearing, shall determine whether there is probable cause to believe that said person committed the offense charged, and shall, in its discretion, either order that the person be discharged, if satisfied that such discharge is consistent with the protection of the public; or, if the court is of the opinion that the interests of the public require that such person be tried for such offense or violation instead of being discharged, the court shall dismiss the delinquency complaint and cause a criminal complaint to be issued. The case shall thereafter proceed according to the usual course of criminal proceedings and in accordance with the provisions of section thirty of chapter two hundred and eighteen and section eighteen of chapter two hundred and seventy-eight. Said hearing shall be held prior to, and separate from, any trial on the merits of the charges alleged.