(dissenting in part). I join the dissenting opinion of Chief Justice Marshall to the extent that it concludes that pretrial detainees (juvenile or adult) retain a privacy interest, protected by art. 14 of the Declaration of Rights of the Massachusetts Constitution, in recordings of their otherwise private conversations, even though they are made by prison officials after notice and in furtherance of a valid penological purpose. That privacy interest includes an interest in the dissemination of the substance of those conversations to persons and government agencies beyond what is necessary to further the limited purpose (institutional security) that justified their interception. I also agree that in order to obtain the recordings of such conversations for the use of the grand jury, the Commonwealth should be required to make a factual showing (albeit ex parte) sufficient to permit a judge to conclude that there is a reason for the subpoena that is consistent with the legitimate function of the grand jury, and that such subpoena is reasonable in scope.