TULSA, Oklahoma - A 1-year-old girl has died from her injuries in what Tulsa police call one of the worst child sex abuse cases they've ever seen.

Officers arrested the boyfriend of the girl's mother early Sunday morning. Cody Alan Johnson, 30, initially was booked into the Tulsa jail Sunday on complaints of child physical abuse and child sexual abuse, both after former felony conviction.

By evening, a first-degree murder complaint was added against him.

Police said 16-month-old Sawyer Jefferson was unconscious when she was brought into the emergency room Saturday night. She never regained consciousness.

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Police said the child's mother came home on Saturday to find her daughter bleeding. She shares a condo with Johnson, near 66th and Memorial.

Investigators say Johnson called the mother to tell her to come home from work because her daughter was badly hurt.

Johnson made up a story to go with the toddler's injuries, officers said.

Officers said the child was unresponsive and in cardiac arrest.

The toddler had "numerous visible facial contusions and bruising and bleeding coming from both the child's vagina and rectum," the police report states. The only explanation given was that the child "slipped on her pajamas and fell on a toy," the arresting officer said.   

The child's mother took her to the emergency room at Saint Francis, where the hospital staff said they immediately realized the story was a lie. The child had to be placed on life support.

TPD Corporal Greg Smith, who leads the department's child crisis unit, spoke to News On 6 on the phone.

He said this is among the worst abuse cases he's seen.

"We've seen some pretty badly beaten and abused kids over the years, but this one's pretty bad. I mean, it is pretty bad," Smith said.

Police said Johnson was the only one home with the child, and they have no reason to believe the child's mother knew about the abuse.

That's why she was not arrested.

“Often times, we find these type of situations where we find some volatility in these relationships, maybe domestic issues, but I don't know of any in this case," Smith said.

Police said they still are waiting to test Johnson's DNA.