PHOENIX -- Deputies at the Maricopa County Sheriff's Office's Fourth Avenue Jail should have noticed something was up in the moments leading up to a 15-minute beating that left one inmate dead, a former member of the Aryan Brotherhood said.

"They should have seen what was going on," the 5 Investigates source said. "They should have looked at that video and said, 'Hmm … something's not right.'"

On May 1, jail inmate Pete Van Winkle, an accused member of the Aryan Brotherhood, assaulted fellow inmate Robert Cotton for 15 minutes. It took five minutes for guards to arrive at the scene, and Cotton died from his injuries.

Surveillance cameras taped the entire episode; however, the guard watching the monitors was talking on the phone at the time of the assault, and he did not have the view from this camera on any of the television screens.

After preparing a 569-page report, deputies concluded that there was nothing the guard could have done.

"After reviewing this incident we are certain that this homicide could not have been prevented," said MCSO Chief of Custody Jerry Sheriden.

After watching the tape, 5 Investigates' source disagreed based on his insider knowledge of the Aryan Brotherhood.

The man joined the gang when he was an inmate in California; he has no direct knowledge of the incident.

Because the source has renounced his membership in the Aryan Brotherhood, he is danger; 5 Investigates has declined to identify him for his safety.

He said the beating looked like something that orchestrated by the Aryan Brotherhood, and it looked like Van Winkle told Cotton he was going to take a beating because he refused to beat up another inmate.

In the video, Cotton appears to voluntarily walk into Van Winkle's cell.

"That guy went into his cell thinking he was just going to get beat up -- by checking," the source said. "That's what they call it. You know, 'Hey, you're just going to get a checking brother. We're just going to lump you up a couple of times. We're good; you'll come back to the yard.' That kind of thing."

The source told 5 Investigates that the prison guards should have paid closer attention to the surveillance tapes.

The crux of his argument lies in footage from right before the beating occurred -- five inmates standing in a circle and having a heated argument.

"It was basically a court," the source said.

In a press conference, Sheridan said the inmates were not holding court; he pointed to the races of the three other inmates as proof of this. One inmate was Hispanic, and the other two were African-American.

"(The Aryan Brotherhood) is a white supremacist gang," Sheridan said. "There is no way on God's earth that these Aryan Brotherhood members -- white supremacists -- would involve these inmates in any fashion."

5 Investigates' source disagreed.

When he was a member of the gang, it was common for other ethnic groups in a cell block to be notified and told to stay away when something was about to happen, he said.

This may explain why one of the men in the circle walked right by the cell during the assault, yet did not alert the guards.

Still, the source said the guards should have known that something was going to happen.

"If there was someone there watching that video in the rec yard with all of those shot-callers there, that should have been a sign -- something's going down," he said.