MOUNT CLEMENS, Mich. -

A 13-month-old girl is in very critical condition in what investigators have called one of the worst child abuse cases they have seen in their careers.

"Twenty-three years of being a police officer, this is one of the most horrific cases of child abuse and sexual abuse that I've seen," said Macomb County Sheriff's Lt. Liz Darba.

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Macomb County Sheriff's officials arrested David Montaldi, 31, on two counts of sexually assaulting the baby girl and a charge of child abuse.

Investigators said the baby was being cared for by Montaldi on Sunday night when something went wrong. Montaldi, who is the child's mother's boyfriend, called her and said his 150 pound bull mastiff dog must have sat on the child. Police said they don?t believe his story.

The mother rushed home, saw her daughter?s injuries and called 911, according to police.

?The deputy at the scene observed bruising to the infant's face and head," said Lt. Darba.

The child suffered three to four skull fractures and is being treated at Children?s Hospital of Michigan in Detroit.

Police said the victim?s mother and Montaldi began dating six months ago and they worked together at Mount Clemens Regional Medical Center, where Montaldi was a resident until this past October.

Montaldi appeared in court Monday afternoon to face charges.

The details of the charges brought this response from the Macomb County judge:

"The pictures are horrendous and this child sustained incredible abuse to the point of almost looking like torture," said Judge Linda Davis.

Davis denied bond for Montaldi. He will remain in the Macomb County jail until his next court appearance. If convicted, he could spend life in prison.