An Oklahoma man accused of killing his stepfather with an "atomic wedgie" has pleaded guilty to manslaughter.

Brad Davis, a 34-year-old former Marine, was arrested in December 2013 after an altercation with his stepfather, Denver St. Clair, 58. In the confusion of the fight, Davis performed the "atomic wedgie," a bullying maneuver in which the waistband of the underwear is pulled up over the head of the victim.

The band pressed against the front of St. Clair's neck, cutting off his air supply, before Davis knocked him unconscious, The New York Daily News reported.

Davis was originally charged with first-degree murder, but reached a plea agreement and pleaded guilty to manslaughter on Monday. He admitted he killed St. Clair "in the heat of passion while defending myself in a fight that got out of hand and went too far," according to The Oklahoman.

Davis' attorney Bob Wyatt claimed St. Clair had bullied Davis his entire life, and that Davis never intended to kill his stepfather.

"He was just tired of taking it. He had been bullied all his life by this guy," Wyatt said. "When he was interviewed that night, he said, 'Man, I did a horrible thing when I gave him that wedgie.' ...He didn't even really know the guy died."

The fight that was reportedly sparked by St. Clair calling Davis and his mother "worthless."

Davis had reportedly told a friend earlier that he was planning to hurt St. Clair that night. Investigators also saw photographs from Davis' cell phone, which indicated that the crime scene had been altered, The Shawnee News-Star reported.

Early in the case, there was some question as to whether the cause of death had been from the atomic wedgie, or from blunt force trauma to his head afterwards. St. Clair's niece claimed that Davis wanted people to think it was the wedgie in order to "disgrace" her uncle.

An autopsy confirmed, however, that it was St. Clair's torn blue underwear cutting off his air that caused his death.

Davis is set to be sentenced in July. Judge John G. Canavan Jr. will choose a prison term between four years and a maximum of 35 years, which was recommended by the prosecution.