PITTSBURGH -- A 10-month-old baby died after being raped and beaten by her mother's boyfriend while the mother was at work, police said.

Da'Niyah Marie Jackson died at Children Hospital on Saturday afternoon, two days after the alleged assault. The Allegheny County medical examiner's office Sunday ruled her death a homicide, saying she died from multisystem organ failure precipitated by her injuries and the assault.

Now, Clinton Smith, 30, the mother's live-in boyfriend, is facing homicide charges after previously being charged with rape and other offenses.

The mother told police she left the baby with Smith on Thursday morning when she went to her waitressing job. The mother found the baby unresponsive when she returned home at about 9:30 p.m. and called paramedics. The baby had severe bruises on her face, arms and legs, as well as a bite mark on her chest, police said. Doctors told police she had also been sexually assaulted.

Smith, who was also caring for his 2-year-old son, told police he did not know how the baby was injured, authorities said. A preliminary hearing in the case was scheduled for Wednesday.