Mass. Gen. Laws ch. 126 § 2
When the commissioners or any of them visit any of said prisons, the sheriff, superintendent, keeper or other officer in charge thereof shall admit them, when required, into every apartment of such prison, exhibit all books, precepts, documents, accounts and papers relative to the affairs of the prison or to the detention or confinement of any person therein, which may be required, and give such aid as they request in the performance of their duties. The commissioners or their committee may examine on oath, administered by one of them, either by written interrogatories, to be answered in writing and subscribed, or otherwise as they may direct, any officer, keeper or other person relative to the affairs or management of any prison, and they may also converse with any prisoner apart, and without the presence of any officer or keeper.
Mass. Gen. Laws ch. 126, § 2