In a tragic incident in Humboldt, Tennessee, a 12-year-old girl has been charged with murder after allegedly strangling her 8-year-old cousin during an argument over an iPhone. The incident, which occurred on July 15, was captured on a security camera in the bedroom the two girls shared.

The footage reportedly shows the older girl using bedding to strangle her younger cousin while she slept in the top bunk. After the fatal act, the older girl allegedly cleaned up the crime scene and moved the victim’s body.

Authorities say the argument began after the girls, who were visiting their grandmother, disagreed on the phone. The suspect has been charged with first-degree murder and tampering with evidence.

Gibson District Attorney Frederick Agee described the act as “one of the most disturbing violent acts” his office has ever prosecuted. He also said he will seek to have the girl tried as an adult to receive a more severe sentence, either through incarceration or supervision.