CREIGHTON, Mo. -- A Cass County father said a lack of sleep sent him over the edge and he now faces assault charges against his 3-month-old baby.

The young father works nights and cares for his daughter during the day.

He told investigators he hasn't been getting much sleep.

They say the actions that resulted from that are criminal.

"We let this boy into our house and never dreamed this would happen," Barbara Sites, the baby's grandmother, said.

Sites said her daughter's boyfriend seemed like a loving and doting father to the couple's baby girl. She let the couple move into her home.

"I was amazed as young as he was he doted on her. He was good to her," Sites said.

Brian J. Kariuki, 20, was charged Wednesday with first-degree assault.

According to doctors at Children's Mercy Hospital, the baby has fractures to her ankles and ribs, traumatic brain injury and extensive retinal hemorraging.

According to court documents, Kariuki first told investigators the baby fell off the couch, but when questioned further he said the baby wouldn't stop crying because of an earache. Kariuki said he started rocking the baby and the harder he would shake her, the more she seemed to settle down.

Sites said she heard her granddaughter screaming. She found Kariuki sleeping and the baby was having seizures. Sites and her daughter rushed the baby to the hospital.

Kariuki is in police custody. The baby remains hospitalized.