Section 13F. Whoever commits an indecent assault and battery on a mentally retarded person knowing such person to be mentally retarded shall for the first offense be punished by imprisonment in the state prison for not less than five years or not more than ten years; and for a second or subsequent offense, by imprisonment in the state prison for not less than ten years. Except in the case of a conviction for the first offense for violation of this section, the imposition or execution of the sentence shall not be suspended, and no probation or parole shall be granted until the minimum imprisonment herein provided for the offense shall have been served. This section shall not apply to the commission of an indecent assault and battery by a mentally retarded person upon another mentally retarded person.

Whoever commits an assault and battery on a mentally retarded person knowing such person to be mentally retarded shall for the first offense be punished by imprisonment in a house of correction for not more than two and one-half years or by imprisonment in the state prison for not more than five years; and, for a second or subsequent offense, by imprisonment in the state prison for not more than ten years. This section shall not apply to the commission of an assault and battery by a mentally retarded person upon another mentally retarded person.