501 CMR, § 10.03
For the purposes of 501 CMR 10.00, the following words shall have the following meanings:
Board. The Witness Protection Board, comprised of the Secretary of Public Safety, the Attorney General, the Auditor, a chief of police appointed by the Massachusetts Chiefs of Police Association, and a district attorney appointed by the Massachusetts District Attorneys' Association, or any member's respective designee.
Critical Witness. Any person who:
(a) is participating in a criminal investigation; or
(b) has received a subpoena in the context of a criminal investigation; or
(c) is reasonably expected to give testimony and, in the judgment of the prosecuting officer, is essential to a criminal investigation or proceeding. For purpose of 501 CMR 10.00, the term "person" shall mean the critical witness, or that witness's relatives, guardians, friends, or associates who are endangered by the witness's participation in the criminal investigation or proceeding. For purpose of 501 CMR 10.00, the term "essential" shall mean the prosecuting officer has a reasonable basis for believing that the witness will provide material, relevant information or testimony.
Prosecuting Officer. The Attorney General or a District Attorney for any district.
501 CMR, § 10.03