Memphis police say a 14-year-old boy has been charged with first-degree murder in the death of a 6-year-old girl who was left in his care.

Police said in a news release Thursday that the charge was filed after the medical examiner's office confirmed her death will be ruled a homicide. The girl died Sunday.

Memphis police spokeswoman Karen Rudolph said Wednesday that the teenager assaulted two girls, ages 6 and 9, and a 7-year-old boy in a home Dec. 23. Rudolph said the teenager had been caring for the children while their foster mother was working. The reason for the attack wasn't clear.

The teenager had been previously charged with attempted murder, child abuse and assault.

The other children were put under the care of the Department of Children's Services.

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