Since arriving at Rikers in March 2015, Mr. Delgado says he has spent about 40 days in solitary. At times, he said, life in the box could be a relief from the violence of the regular population.

“I was fighting the whole week,” he said. “So, I’m like, damn, finally a break. I used to wake up, and breakfast is like 4, 5 in the morning. So you got to fight for your cereal, so I’m like I didn’t even brush my teeth. My heart is pumping, and I got to get ready. I don’t know what’s about to happen but it’s about to go down. I was exhausted.”

That feeling of safety lasted for only a few hours, he said. Other inmates yelled constantly, and he missed privileges like commissary and three daily phone calls.

Mr. Delgado has been in and out of Rikers since he was 16, mostly short stints for drugs and other minor crimes. This time he is potentially facing a decades-long sentence for the murder of a 21-year-old man in Queens.

“I think about it — damn this could be the rest of my life,” he said. “That’s why I got to have a radio or something to keep my mind off that, talk to someone.”

He looks forward to his girlfriend’s visits. “She keeps me at peace. She reminds me of what I got in the town.”

Because he is constantly in trouble, he and his girlfriend are separated by a glass partition during visits. He has not kissed her since September.