(a) If in the opinion of the court the interest of justice would be served by relieving the eligible youth from the onus of a criminal record and by not imposing an indeterminate term of imprisonment of more than four years, the court may, in its discretion, find the eligible youth is a youthful offender; and

(b) Where the conviction is had in a local criminal court and the eligible youth had not prior to commencement of trial or entry of a plea of guilty been convicted of a crime or found a youthful offender, the court must find he is a youthful offender. 2. Where an eligible youth is convicted of two or more crimes set forth in separate counts of an accusatory instrument or set forth in two or more accusatory instruments consolidated for trial purposes, the court must not find him a youthful offender with respect to any such conviction pursuant to subdivision one of this section unless it finds him a youthful offender with respect to all such convictions. 3. Upon determining that an eligible youth is a youthful offender, the court must direct that the conviction be deemed vacated and replaced by a youthful offender finding; and the court must sentence the defendant pursuant to section 60.02 of the penal law. 4. Upon determining that an eligible youth is not a youthful offender, the court must order the accusatory instrument unsealed and continue the action to judgment pursuant to the ordinary rules governing criminal prosecutions.