Gilbert Ray Postelle was born on June 22, 1986, in Oklahoma. He was abandoned by his mother at a young age and grew up in an environment shaped by drug use and instability. By the age of twelve, Postelle was using methamphetamine daily. Police records show he was arrested at least eight times in Midwest City for drug manufacturing and weapons violations before the age of twenty.

His father, Earl Bradford "Brad" Postelle, had a 1996 drug conviction and was suspected in 1999 of manufacturing methamphetamine in a school bus behind his home. Although Brad was charged with endeavoring to manufacture meth and drug possession, those charges were dropped. By the early 2000s, Brad suffered a severe brain injury from a motorcycle accident, resulting in seizures and behavioral changes. Gilbert grew up in this volatile environment with heavy drug use and his father’s criminal activities as a constant influence.

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.