In Carney v. City of Springfield (1988), the Massachusetts Supreme Court ruled that it was improper to discharge an officer without providing a promise of full "transactional immunity."
Massachusetts is the only state that requires that a public employee be granted transactional immunity before being compelled to answer questions. "Transactional immunity" is different from "use immunity," which is guaranteed by your Garrity rights. Transactional immunity protects you from prosecution for the offense or offenses involved.
Carney "Right to Remain Silent" Statement
"Because I am accused of behavior that could form the basis of criminal action against me and/or my responses could tend to implicate me in a criminal action, I assert my right under Article 12 of the Mass. Declaration of Rights and Carney v. Springfield to remain silent without fear of retribution. I refuse to answer all questions unless and until I receive transactional immunity for all crimes that may arise from this investigation."