An 8-year-old boy is being charged with beating a 1-year-old girl to death while they were left home alone as their mothers went to a nightclub, Alabama police said Tuesday.

Birmingham police spokesman Sean Edwards said the boy beat and killed 1-year-old Kelci Lewis when she wouldn’t stop crying. The mother of the toddler, 26-year-old Katerra Lewis, also is charged with manslaughter for her role in the death of her daughter.

“This is by far one of the saddest cases that I have witnessed and been a part of since I became a police officer,” Edwards said. “This type of irresponsibility on behalf of a parent is totally unacceptable,” he said.

Police said a murder warrant has been obtained for the boy who is now in the care of Alabama’s child welfare agency, the Department of Human Resources. His case will go through the family court system.

Edwards said the 8-year-old was the oldest of six children left alone as their mothers, Katerra Lewis and a friend, went to a nightclub on the night of Oct 11. The 8-year old is the son of Katerra Lewis’ friend. The friend has not been charged.

A 6-year-old who was in the home that night told police what happened, Edwards said, and the information was consistent with the toddler’s injuries. Kelci Lewis suffered severe head trauma and major damage to her internal organs, police said.

Edwards said the 8-year-old is the youngest murder defendant he’s ever been aware of in the Birmingham area.

“I believe the 8 year-old is going to require some intense counseling for the next several years,” Edwards said.

He said the mother’s punishment is “something she has to live with for the rest of her life.”

Katerra Lewis has posted $15,000 bond.