Bronx police arrested a woman and her boyfriend on Tuesday for allegedly beating her 4-year-old son to death.

Alicia Smith, 26, was arrested on a manslaughter charge for the death of Quachon Brown. Her boyfriend Jose Calderone, 18, faces a second-degree murder charge.

Investigators say Calderone admitted to physically abusing the child. "He has made statements saying he lost his temper and hit the child," says the official, who spoke on condition of anonymity to the press.

The 6-and 9-year-old siblings of the victim told investigators they had seen Calderone beating the boy.

The anonymous official said bruises on the victims body were "consistent with beating with a fist."

Preliminary evidence suggest the boy had a fractured skull, a damaged liver and atrophied leg muscles, reports the AP.