Whoever has reason to believe that another person is deprived of his liberty or held in custody in violation of the preceding section may file a petition, on the oath of the petitioner, in the probate court for the county where such person is believed to be detained, stating his name, age and general description, where, when and under what circumstances he was deprived of his liberty, where he is believed to be detained, the name of the person so depriving him of his liberty, if known, the name of his supposed custodian and any other material facts and circumstances.
Massachusetts Legal Code