Little Kelci Lewis suffered severe head trauma and "major internal organ damage," leading to her death, police said in a statement.
"We did have some information that the 8-year-old got extremely agitated because the 1-year-old refused to stop crying, and so I guess the 8-year-old took it upon himself and began to commit violent acts against the 1-year-old," Lt. Sean Edwards of the Birmingham Police Department told reporters Tuesday.
The girl's mother, 26-year-old Katerra Lewis has been charged with manslaughter, police say. She is out of jail on a $15,000 bond. The 8-year-old's case will be handled in juvenile court, authorities say, where criminal charges are not allowed. He is in the custody of the state.
Police say Lewis and her roommate, a mother of five, went out about 11 p.m. on October 10. Lewis left Kelci under the supervision of her roommate's children, all far too young for the responsibility, police said.
Lewis and the roommate didn't check on the kids when they got home from clubbing about 2 a.m., according to police.
Kelci was unresponsive the next morning when Lewis found her in her crib, where the boy had placed her. Police didn't receive a call until about 10:30 a.m., Edwards said. The Jefferson County coroner ruled the death a homicide.
Had the women checked on the children when they got home from the club, Edwards said, police and paramedics would have responded earlier and Kelci's death might have been averted.
"The sad part is you had an adult mother here who had the audacity to leave her 1-year-old in the custody of several other children at the house and none of those kids were over the age of 8," Edwards said.
The children were all between 2 and 8 years old, and only one of them was able to provide the "key information" about what happened to Kelci, Edwards said.
Emory Anthony, Lewis' attorney, told CNN affiliate WBRC
that manslaughter is applicable when someone acts recklessly or in the heat of passion, not when they allow someone else to act in a dangerous manner.
"I think they are trying to allege that she was reckless or negligent in some particular way, and we'll have to deal with that. Of course, my client has a different story about what transpired," Anthony told the station.
It's unclear if the mother of five will face charges -- Mary Russell, the Jefferson County prosecutor handling the case wouldn't say, according to WBRC.
Her other four children are in Department of Human Resources custody, the station reported.
For Katerra Lewis, the cost could go well beyond any possible sentence she could receive on a manslaughter conviction.
"I think her punishment is going to be something she'll have to live with the rest of her life, her actions that night, choosing the club over taking care of her 1-year-old," Edwards said.