Ruben Montoya Cantu was born on December 5, 1966, in San Antonio, Texas. He lived with his mother and father until he was 14 years old. At that age, his parents separated. His mother moved 20 miles away, while Ruben stayed behind with his father. They lived in a trailer in a neighborhood known for its crime in south San Antonio.

This area was home to a group of tough kids called the Grey Eagles. Despite being smaller than many of his peers and attending special education classes, Ruben became a leader among them. By the time he turned 15, he was involved in stealing cars for an organized auto theft ring. He often drove the stolen cars to Mexico for cash and spent days doing so.

While the police department in San Antonio faced scandals involving corruption, Ruben was busy avoiding law enforcement while stealing cars. His older brothers had previous run-ins with the law, having been arrested for drug and theft charges. However, Ruben had multiple encounters with the police but was never convicted of anything before an incident that occurred in November 1984.

On the night of November 8, 1984, Ruben Montoya Cantu, who was 17 years old at the time, and his friend David Garza, who was 15, broke into a house in San Antonio. The house was under construction. Inside, they encountered two men, Pedro Gomez and Juan Moreno, who were sleeping on the floor. Cantu and Garza held the two men at gunpoint and robbed them of their wristwatches and cash.

During the robbery, Gomez attempted to reach for a hidden pistol. In response, Cantu shot Gomez multiple times, which resulted in his death. Moreno was also shot several times but survived the attack. After the shooting, Cantu and Garza fled the scene.

Initially, there were few leads in the case. The surviving victim, Juan Moreno, could only provide a vague description of his attackers. Police conducted interviews, but there was no immediate identification. Several days later, Moreno had difficulty identifying anyone from a series of photographs shown to him because of his injuries.

Approximately four months later, Cantu shot an off-duty police officer named Joe De La Luz in a bar. This incident led to renewed interest in the earlier murder case. Moreno was questioned again and, after multiple attempts, eventually identified Cantu as one of the attackers. David Garza, Cantu's co-defendant, later testified and admitted to being at the scene of the crime but insisted that Cantu was not the person who shot the victims.

Cantu was tried and convicted for his role in the robbery and murder. He maintained his innocence throughout the trial and after his conviction. He was executed by lethal injection on August 24, 1993, becoming one of the youngest individuals executed in Texas. After Cantu's execution, several individuals, including the surviving victim, recanted their testimonies. There have been ongoing discussions and debates about the fairness and correctness of the trial and conviction.