Gilbert Ray Postelle was born on June 22, 1986, in Oklahoma. From a young age, his life was marked by hardship. His mother abandoned him when he was a child. This left a significant impact on his upbringing. By the time he was twelve, he started using methamphetamine daily. This began a cycle of substance abuse that would define much of his early life.

As he grew older, Postelle faced increasing legal troubles. He was arrested at least eight times in Midwest City for various offenses related to drug manufacturing and weapons possession. These arrests were linked to the environment he was raised in. His father, Earl Bradford "Brad" Postelle, had a criminal history himself. In 1996, he was convicted of drug-related charges and was later suspected of manufacturing methamphetamine in a school bus parked behind their home in 1999. Though he was charged with drug possession and attempting to manufacture drugs, the charges were eventually dropped.

On May 30, 2005, Gilbert Ray Postelle, along with his brother David, father Brad, and another man named Randall Wade Byus, committed a violent crime in Oklahoma City. This day was Memorial Day, and the group was involved in a "blitz attack" that led to the deaths of four people: Donnie Swindle, James Alderson, Terry Smith, and Amy Wright.

The attack was driven by Postelle's mistaken belief that Donnie Swindle was responsible for an accident that severely injured his father. During this assault, the four victims were taken outside a trailer home, where they were ordered to kneel. Postelle fired over thirty rounds from an AK-47 rifle at close range, hitting all four victims. As they attempted to escape, he shot two of them from behind.

After the crime, investigators traced a maroon van linked to the incident to Terre Haute, Indiana. Police were able to find evidence from this vehicle and arrested several individuals. Gilbert Postelle was arrested the day after the attack, on August 17, 2005. His brother David and father Brad were arrested shortly before him.

Postelle was tried and found guilty of murder in 2008. He received two death sentences, one for Amy Wright and one for James Alderson, alongside a life sentence without the possibility of parole for the murders of Donnie Swindle and Terry Smith. His brother faced a similar fate, while their father was declared incompetent to stand trial.

After years of legal proceedings, the Oklahoma Court of Criminal Appeals upheld Postelle's death sentence in December 2011. In the following years, he became involved in multiple lawsuits related to the death penalty and the methods of execution in Oklahoma.

Finally, Gilbert Postelle was executed by lethal injection on February 17, 2022. At the time of his execution, he declined to say any last words, and his last meal consisted of various McDonald’s items.