PHOENIX -- Guards at the Maricopa County Jail may have missed warning signs that one inmate was going to kill another, 5 Investigates found.

On May 1, inmate Pete Van Winkle attacked fellow inmate Robert Cotton -- beating, strangling and jumping on the victim's head for nearly 20 minutes, surveillance footage shows.

Detention officers said once they spotted Van Winkle dragging Cotton out of his cell, they rushed to the scene within seconds; the footage, however, shows it took the guards an additional five minutes to reach Van Winkle.

5 Investigates discovered the guard who was supposed to be monitoring the security cameras was talking on the telephone at the time.

• READ: Video Contradicts MCSO's Version Of Jail Slaying | WATCH: Video Shows Man Slain In MCSO Jail

The slaying appears to have been a "hit" ordered by the Aryan Brotherhood against Cotton because Cotton refused to beat up another inmate, according to the official incident report prepared by the Maricopa County Sheriff's Office.

Van Winkle has been charged with first-degree murder, and he is facing the death penalty. Officials have not charged anyone else in connection with the death.

According to security consultant and former police officer Jess Torres, Van Winkle could now be considered a celebrity in the Aryan Brotherhood, a prison gang known for its violence.

"He's gone from college to pro," Torres said.

Torres also said guards should have kept a close eye on Van Winkle, especially because of his association with the Aryan Brotherhood.

"He would be called, on the street, a person of interest, so I would definitely be focusing on that individual," Torres said.

Additionally, a close reading of MCSO's official report on the slaying reveals that Van Winkle appears to have hinted he would do something bad, as recorded in a phone conversation with his mother.

• READ: MCSO Incident Report Part 1 | Part 2

In the transcript, Van Winkle tells his mother, "You know this guy ... there's something that I got to take care of over there," and there was a possibility he may get his jail privileges revoked because of it.

While detention officers said Van Winkle caused no problems in the jail during the weeks before the slaying, MCSO's press release admits he was a dangerous inmate.

Van Winkle was classified as a high-risk inmate with repeated violations for fighting, threatening and physical assault during a 6-year prison term between 2001 and 2007.

When asked if the guards faced any consequences after Cotton's death, a spokesman for the sheriff's office refused to comment, saying the office would call if they had something to say, before hanging up.