Mass. Gen. Laws ch. 159 § 29
An inspector shall, under the direction of the department, investigate as promptly as may be any accident upon a railroad, railway or motor vehicle of a carrier of passengers under the jurisdiction of the department, or in which such railroad, railway or motor vehicle is concerned, which causes the death or imperils the life of any person, and shall report thereon to the department, which shall investigate the cause of any such accident resulting in loss of life, and may investigate any other accident. The inspector shall attend the inquest held in case of any such death by accident and may cause any person who has knowledge of the facts or circumstances connected with such death to be summoned as a witness to testify at the inquest.
Mass. Gen. Laws ch. 159, § 29