Mass. Gen. Laws ch. 260 § 4B
Actions of tort for bodily injuries or for death or for damages to property against the owner or operator of a motor vehicle, the operator of which failed to make himself or said owner known at the time of the accident or incident out of which such actions arise may, notwithstanding any provisions of law relating to limitations of actions, be commenced within six months after the plaintiff learns of the identity of the defendant; provided, that written notice of the time, place and facts of said accident or incident be given by the person injured or by someone in his behalf to the police and to the registrar of motor vehicles within thirty days after such accident.
No action shall be brought under this section after the expiration of three years from the date on which such accident or incident occurred.
Mass. Gen. Laws ch. 260, § 4B