Mass. Gen. Laws ch. 123A § 15
If a person who has been charged with a sexual offense has been found incompetent to stand trial and his commitment is sought and probable cause has been determined to exist pursuant to section 12, the court, without a jury, shall hear evidence and determine whether the person did commit the act or acts charged. The hearing on the issue of whether the person did commit the act or acts charged shall comply with all procedures specified in section 14, except with respect to trial by jury. The rules of evidence applicable in criminal cases shall apply and all rights available to criminal defendants at criminal trials, other than the right not to be tried while incompetent, shall apply. After hearing evidence the court shall make specific findings relative to whether the person did commit the act or acts charged; the extent to which the cause of the person's incompetence to stand trial affected the outcome of the hearing, including its effect on the person's ability to consult with and assist counsel and to testify on his own behalf; the extent to which the evidence could be reconstructed without the assistance of the person; and the strength of the prosecution's case. If the court finds, beyond a reasonable doubt, that the person did commit the act or acts charged, the court shall enter a final order, subject to appeal by the person named in the petition and the court may proceed to consider whether the person is a sexually dangerous person according to the procedures set forth in sections 13 and 14. Any determination made under this section shall not be admissible in any subsequent criminal proceeding.
Mass. Gen. Laws ch. 123A, § 15