A 12-year-old girl is facing charges including first-degree murder after police in Tennessee said video captured her smothering her 8-year-old cousin to death, reportedly after an argument over an iPhone.

The county's top prosecutor reported the killing took place in a bedroom the cousins were sharing at a home in Humboldt, about 90 miles northwest of Memphis.

Frederick H. Agee, the District Attorney General for the state's 28th Judicial District, which includes Haywood, Crockett and Gibson counties, released in a statement Thursday.

Footage of the crime obtained by the Humboldt Police Department shows the 12-year-old girl use bedding to suffocate her 8-year-old cousin, "while the victim was sleeping in the top bunk of bunk beds they shared."

"After the suffocation, the juvenile cleaned up the victim and repositioned her body," the statement continues.

The slain girl's school in Nashville identified the victim as 8-year-old Demeria Hollingsworth.

According to the prosecutor, the 12-year-old girl turns 13 this week.

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Prosecutor: 'One of the most disturbing violent acts'

Agee said Humboldt police filed a petition of delinquency charging the juvenile with first-degree murder and tampering with evidence.

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

"Due to the horrendous nature of this crime and under Tennessee Law the Juvenile Court loses jurisdiction after a juvenile turns 19, and therefore, the juvenile would be free from any further detention, supervision, or court-ordered mental health treatment, our office is petitioning Juvenile Judge Mark Johnson to transfer the delinquent child to Circuit Court to be tried as an adult."

Under the law, the move would allow for a lengthier sentence, whether through incarceration or supervised release.

Victim's mother: The girls had argued over an iPhone

Police have not released a motive in the killing.

Neither the victim nor the accused juvenile live in Humboldt, according to the release which said both children were visiting family.

On Monday, Metro Nashville Public Schools confirmed to USA TODAY the victim attended school in Music City and would "be greatly missed."

“The Cockrill community is mourning the unexpected loss of Demeria Hollingsworth, a beloved student who had been part of Cockrill since PreK," Cockrill Elementary Principal Casey Campbell confirmed. "Demeria was known for her hard work, intelligence, and sweet demeanor. She was cherished by everyone who knew her. Her passing has left all of us at Cockrill devastated.”

The victim's mother, Rayana Smith told WREG-TV her daughter Demeria and her cousin "had been arguing over an iPhone after coming from out of town to stay with their grandmother." 

“She was very energetic, always happy, outgoing, smart, she made straight A’s she always made the principles list she was my girl, it’s a senseless incident, accident, what we people want to call it, to me a tragedy. She well be truly missed,” Tamara Pullum, Demeria's grandmother told WSMV-TV.

USA TODAY has reached out to the victim's family.

"Please keep the victim’s family and the Humboldt Police Department in your thoughts and prayers," Agee said.

The case remained under investigation by police Monday.

Natalie Neysa Alund is a senior reporter for USA TODAY. Reach her at [email protected] and follow her on X @nataliealund.