Tennessee police were alerted of a chilling home security camera video showing the moments leading up to the killing of an 8-year-old girl. This week, a district attorney’s office filed charges against the perpetrator… whose not too much older than the victim.

The video came from inside a Humboldt home on July 15, according to the Office of the District Attorney General, 28th Judicial District. The victim’s mother, Rayana Smith, told WREG Memphis both the girls were in town visiting their grandmother for the summer. However, SMith said the two got into an argument over an iPhone. Somehow, the argument resulted in an unthinkable act.

Humboldt police reviewed the video and found a 12-year-old juvenile victim climbed onto the top bunk of the bunk beds they shared and used bedding to suffocate her 8-year-old cousin who was asleep. She then cleaned up the girl and repositioned her body, authorities said.

“When they told me about [the iPhone], I should have just gone to get my kid. But they were having fun for the summer and I didn’t think she would kill my baby,” Smith told reporters.

The police department filed a petition of delinquency, requesting the girl be charged with first degree murder and tampering with evidence. District Attorney General Frederick H. Agee said due to the “horrendous nature” of the crime, he is petitioning the juvenile court for the now-13-year-old girl to be tried as an adult which would lead to a heavier sentence than just supervision and mental health treatment.

“I consider this to be one of the most disturbing violent acts committed by either an adult or juvenile that my office has prosecuted,” said Agee in a statement.

The victim’s family organized a GoFundMe to raise money for funeral costs. The girl had just turned eight in April.