Ángel Nieves Díaz was born on August 31, 1951, in Puerto Rico. He became involved in criminal activities and drug use early in life, earning the nickname "Papo la Muerte" ("Daddy of Death"). At 17, he was arrested for heroin possession. By 24, he had escalated to armed robbery, during which he shot and wounded a police officer, leading to a 5–8 year prison sentence.

In July 1978, while serving time, Díaz stabbed the director of a drug rehabilitation center 19 times, resulting in a second-degree murder conviction and a 10–15 year sentence. In 1979, he escaped from the Río Piedras State Penitentiary, nearly killing a guard in the process, and fled to Florida.

On December 29, 1979, Díaz, along with Angel "Sammy" Toro and an unidentified accomplice, robbed the Velvet Swing Lounge, a strip club in Little Gables, Florida. During the robbery, manager Joseph Nagy was shot and killed. Most patrons and staff were locked in a restroom, leaving no direct witnesses to the shooting.

In 1983, Díaz's girlfriend informed police of his involvement. His fingerprint was found on a matchbook at the scene. In 1986, Díaz was convicted of first-degree murder and other charges, receiving a death sentence. He represented himself at trial, despite limited English proficiency, and claimed Toro was the shooter. A jailhouse informant's testimony, later recanted, played a significant role in his conviction.

Díaz maintained his innocence until his execution on December 13, 2006. His execution was notably botched; the lethal injection took 34 minutes, twice the usual time, due to improper needle placement, causing severe chemical burns. This incident led to a temporary suspension of executions in Florida.