On a Saturday evening in July 2013, just before 6:30, James Rhodes was recorded on a surveillance camera walking into a Metro PCS cellphone store in Jacksonville, Fla. He was wearing a black do-rag and a blue bandanna, which he pulled over his nose and mouth. Shelby Farah, the store manager, stood behind the counter. Rhodes pointed a gun at her and demanded the money in the cash register. Shelby gave it to him. Then Rhodes shot her in the head. She was 20 years old. He was 21.

Shelby, the oldest of three siblings in a family of Palestinian descent, was working and planning to start college in the fall. Her mother, Darlene Farah, had been nervous when her daughter started as a manager of the Metro PCS branch, which was in a high-crime part of town, miles from their home near the beach. But Shelby told her mother she felt comfortable in the neighborhood; she’d gone to high school nearby, attending a magnet program on criminal justice. She was nicknamed “peacemaker” in middle school because she couldn’t stand to see kids argue. An accomplished cheerleader, she volunteered for two seasons as a coach for a group of girls instead of pursuing a chance to make the cheerleading squad for the Jaguars football team.

Rhodes, who is black, was placed in foster care at age 5 and went to live at a state boys’ home at 6. He reads at a third-grade level and struggles with simple math. At 17, Rhodes moved to an older cousin’s house with his younger half sister. After a couple of weeks, their cousin disappeared, leaving them without money for food or rent. The landlord evicted them. Within 14 months, Rhodes was arrested for petty theft at Sears, Walmart and Kmart and for jumping and robbing a man with four other boys. At 19, he was jailed for brandishing a gun at two women. Rhodes says he was high when he killed Farah. He told his lawyer, the assistant public defender Debra Billard, that he was sorry for what he had done. In early 2014, Billard told prosecutors that Rhodes would plead guilty in exchange for a sentence of life without parole. Instead, the state was determined to seek the death penalty.

In most of the country, it would be very unlikely for prosecutors to pursue death for a defendant like James Rhodes. Execution is supposed to be a punishment for the “worst of the worst,” Justice David Souter wrote a decade ago. With violent crime falling, and bipartisan concerns about the rising costs of capital murder trials increasing — some states spend an average of $1 million more on litigation for a defendant sentenced to death than on one sentenced to life in prison — the death penalty is on the decline in the United States.