Timothy Rohan headed out from his home in Holyoke, Mass., eight years ago on an unlikely mission. The construction worker planned to shoplift supermarket bags of shrimp, then sell the purloined shellfish to bodegas in the city’s gritty downtown. The cash proceeds would feed his desperate need for fentanyl. The scheme ended abruptly when two police cruisers pulled up beside him, the officers ordering the young man onto the pavement and locking him in handcuffs. A few hours later, guards hauled Rohan from a cell in the local courthouse and brought him before a judge – though he had stolen...