WASHINGTON — A 35-year-old man was executed in the US state of Oklahoma on Thursday for a quadruple murder he carried out at the request of his father when he was a teenager.

Gilbert Ray Postelle was put to death by lethal injection at Oklahoma State Penitentiary in McAlester, Oklahoma, prison officials said.

Media witnesses said the execution appeared to have taken place without any complications.

They said Postelle shook his head no when asked if he had any last words.

Postelle’s execution was the fourth in Oklahoma since October — when a nearly seven-year moratorium on executions was lifted — and the third in the United States this year.

Postelle and his older brother David were convicted of murdering four people in Del City, Oklahoma, in 2005.

Around 60 rounds were fired from assault rifles during the attack on a mobile home where a man named Donnie Swindle was living.

Earl Postelle, the father of the boys, blamed Swindle — mistakenly as it turned out — for a motorcycle accident the previous year which left him severely injured.

Swindle, two other men and a woman who were at the mobile home at the time were killed.

In a hearing before the Oklahoma clemency board in December, Gilbert Postelle said he had been a methamphetamine addict since the age of 13.

“My life at that time was filled with chaos and drugs,” Postelle said. “It was a family addiction.”

“In no way does that excuse my actions,” he added. “I do regret the pain and the loss that I have caused.”

Postelle said he was under the influence of his father, who was declared mentally incompetent because of brain injuries from the motorcycle accident and did not go on trial. He has since died.

“My dad was everything to me, even with all of his flaws,” Postelle told the clemency hearing.

Postelle’s brother David was sentenced to life in prison without possibility of parole for his role in the slayings.

The other man involved, Randal Wade Byus, cooperated with the authorities and was sentenced to six years in prison.

A series of botched executions in Oklahoma led to a temporary moratorium on capital punishment in the state in 2015, but the moratorium was lifted in 2021.

The US Supreme Court struck down the death penalty in 1972 but reinstated it four years later.

The number of executions carried out annually in the United States has been declining in recent years.

Capital punishment has been abolished in 23 US states, while three others — California, Oregon and Pennsylvania — have observed a moratorium on its use.