"The 13-year-old reported he started to wrestle with the victim and practiced 'WWE' style wrestling moves on the 5-year-old," Col. John Fortunato of the Jefferson Parish Sheriff's Office said in a news release Tuesday.
Those moves allegedly included repeatedly slamming the girl on a bed, punching her in the stomach, jumping on her and striking her with his elbow. A coroner's investigation found the girl died of multiple injuries, including broken ribs, lacerations of the liver and internal bleeding.
In a statement released Tuesday, WWE offered condolences to the victim's family but cautioned against attributing the death to its industry.
"Authorities have already charged the accused with second-degree murder and determined that this was not an accidental death due to a wrestling move," the organization said.
"As in similar cases, criminal intent to harm and a lack of parental supervision have been the factors resulting in a tragic death."
The boy had been left to babysit the girl by his stepmother when the alleged beating occurred, authorities said. After the beating, the girl later complained of a stomach ache. When she stopped breathing, the boy called 911. Emergency responders could not revive her and she was pronounced dead at a hospital.
The boy was taken to a juvenile facility and booked on a second-degree murder arrest warrant after he was interviewed by homicide Detective Matt Vasquez.
Authorities released the name of the suspect but The Associated Press generally doesn't identify juveniles charged with crimes.
The detective said the boy told him that he knew the wrestling moves on TV were fake, but he was smiling and appeared to enjoy talking about them.
"The 13-year-old continued by saying the victim complained that she was hurting, but he continued to slam, punch and elbow her for an additional two or three minutes, stopping when his mother called him on the phone to check on he and the victim," sheriff's officials said in the news release.