Teghan Alyssa Skiba died at UNC Hospitals Monday night.
Deputies say 21-year-old Jonathan Douglas Richardson took the girl to the Johnston Medical Center on Friday claiming she fell out of bed. But doctors called authorities when they discovered human bite marks, bruises, cuts, severe head trauma and evidence of extreme sexual abuse.
Sheriff's investigators took out search warrants just hours after the case was reported to them.
Richardson was supposed to be caring for the child while his girlfriend attended military training with the Army National Guard in New Mexico
According to search warrants, Richardson shared the same air mattress with the girl in an outbuilding behind Richardson's grandparent's house on the outskirts of Smithfield near Brogden. There was no running water and no bathroom.
The search warrants state Richardson told detectives he "lost it" when the little girl urinated and defecated in their shared bed.
He said he whipped her with an electrical cord.
He also stated he was bipolar and 'little things set him off."
Detectives searched took dental impressions and DNA evidence from Richardson and searched his pickup truck, a room in his grandparent's house, and the outbuilding where he was staying with the child.
Among the items they collected were drug paraphernalia and a "green leafy substance" along with a shotgun, rifle, knives, clothing and multiple other items.
The warrants also include graphic details of sexual abuse that could make a case for the death penalty.
Johnston County Sheriff Steve Bizzell told ABC11 Monday that 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.
The warrants state Skiba's mother Helen Reyes left for New Mexico July 6.
Family members said Tuesday that Reyes did not want to speak to the media, because she is too upset. They did say, however, she is cooperating with the investigation.
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.
"The mother knew when she went off for training what environment she was leaving that child in and that was a barn with no running water, no bathroom," Bizzell said. "She was scared of this guy herself, but yet goes off and leaves this child in an environment of that nature, she's got some responsibility also."
The sheriff also indicated that anyone with responsibility in the case could face charges.
"We all just fell in love with a little girl that we'd never known before, because of the sensitive nature of a young child having to go through all of this abuse," Bizzell said.
Richardson is charged with first-degree murder and is being held without bond in Johnston County Jail.
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 and more charges could be filed.