There is no "expungement" law in Massachusetts. The two legal remedies available for people convicted of crimes in Massachusetts are obtaining a pardon, or having their criminal records sealed.
Pardons are governed by the Massachusetts State Constitution:The effect of a pardon is described by Massachusetts statute: MGL 127, § 152Art. VIII. The power of pardoning offences, except such as persons may be convicted of before the senate by an impeachment of the house, shall be in the governor, by and with the advice of council, provided, that if the offence is a felony the general court shall have power to prescribe the terms and conditions upon which a pardon may be granted; but no charter of pardon, granted by the governor, with advice of the council before conviction, shall avail the party pleading the same, notwithstanding any general or particular expressions contained therein, descriptive of the offence or offences intended to be pardoned.
Having a criminal record sealed is govered by statute, MBL 276, § 100A - although there is a lengthy waiting period described in that statute before application is possible. The effects of having a record sealed are described at MGL 276, § 100C