“John MacKenzie was no ordinary prisoner. In the more than 40 years he spent behind bars, he became one of the most respected inmates in the state’s penal system. He had a spotless disciplinary record. He took full responsibility for the murder of Mr. Giglio. He earned degrees in business and the arts. He started a program to give victims the opportunity to speak directly to inmates about the impact of their crimes. The state’s own risk-assessment program found that he posed little to no risk of re-offending. Prison guards, judges, clergy members and prosecutors wrote letters supporting him.”