Mass. Gen. Laws ch. 248 § 11
The person in whose custody the prisoner is found shall state in writing, plainly and unequivocally, to the court or justice before whom the writ is returnable
First, Whether the prisoner is in his custody or power or under his restraint.
Second, If the prisoner is in his custody or power or under his restraint, his specific authority for and the true and whole cause of such imprisonment or restraint, with a copy of the writ, warrant or other process, if any, upon which the prisoner is detained.
Third, If the prisoner has been in his custody or power or under his restraint, and has been transferred to that of another, particularly to whom, when, why and by what authority such transfer was made.
The statement shall be signed by him and, unless he is a sworn public officer and makes the statement in his official capacity, shall be sworn to by him.
Mass. Gen. Laws ch. 248, § 11