A defendant who intends to offer evidence of mental retardation that would preclude the imposition of a sentence of death shall file with the clerk of courts not later than 90 days after arraignment, or within such other time as allowed by the court upon cause shown, a notice of the intention to offer the evidence and certification of service on the attorney for the Commonwealth.

A defendant who intends to introduce expert evidence relating to mental retardation that would preclude imposition of a sentence of death shall file with the clerk of courts not later than 90 days after arraignment, or within such other time as allowed by the court upon cause shown, a notice of the intention to offer the expert evidence and a certification of service on the attorney for the Commonwealth.

Within 30 days after receipt of the defendant’s notice of mental retardation that would preclude the imposition of a sentence of death or notice of expert evidence of mental retardation or within such other time as allowed by the court upon cause shown, the attorney for the Commonwealth shall file and serve upon the defendant’s attorney, or the defendant if unrepresented, written notice of the names and addresses of all witnesses the attorney for the Commonwealth intends to call to disprove or discredit the defendant’s claim of mental retardation.