Deputies say 21-year-old Jonathan Douglas Richardson took the girl to the Johnston Medical Center claiming she fell out of bed. But doctors called authorities when they discovered human bite marks, bruises, cuts, severe head trauma and signs of possible sexual abuse.
Skiba was later air-lifted to UNC Chapel Hill Hospital for further treatment, but died of her injuries on Monday around 6:30 p.m.
Johnston County Sheriff Steve Bizzell told ABC11 earlier in the day that her condition was not improving and she remained in critical condition.
Bizzell said the abuse likely happened over several days and called it one of the worst cases of abuse his investigators have ever seen.
"The reality is probably 10 times worse than anyone could possibly imagine," he said Monday.
Richardson was supposed to be caring for the child while his girlfriend, Skiba's mother, was in New Mexico for Army Reserve training.
On Friday, Helen Reyes returned from training in New Mexico to be at her daughter's side in the hospital.
But Bizzell said he feels the girl's mother has some responsibility for what happened because she knew the conditions she was leaving her child in.
Bizzell said the couple was living with the child in an air conditioned barn behind the home of Richardson's grandparents on the outskirts of Smithfield near Brogden. There was no running water, no bathroom, and just a single air mattress on the floor to sleep on.
Investigators have not charged Richardson's grandparents with any crime, but Bizzell said it's likely more charges will be filed.
Richardson is now charged with first degree murder and is being held without bond in Johnston County Jail.
Earlier on Monday, Richardson faced a judge in Smithfield for the first time. He was originally charged with felony child abuse with severe bodily injury and held in jail under a $1 million bond.
In the meantime, authorities say further investigation into Skiba's death is ongoing by the JCSO, Johnston County District Attorney's Office, and the N.C. Chief Medical Examiner's Office.