The toddler had only been with his mother's boyfriend for about 75 minutes Thursday morning before South St. Paul police were called to the apartment.

Officers found the 15-month-old boy lying on the living room floor. Medics rushed him to Children's Hospital of St. Paul, where the boy had emergency brain surgery. He had swelling and bleeding on his brain that required doctors to remove a piece of his skull. His liver was lacerated in four places, causing internal bleeding. He had bruises on his face, abdomen, back and buttocks. One of the bruises on his buttock was in the shape of a hand.

The boyfriend, 21-year-old Lamar J. Crump, has been charged in Dakota County District Court with first-degree assault and malicious punishment of a child, both felonies. He is being held in the county jail on $300,000 bail or $100,000 with conditions.

According to the charging document, the boy's mother left her son with a neighbor, his regular caretaker, Wednesday night because the mother worked overnight.

That woman returned the boy to Crump about 5 a.m. Thursday. She said the boy was fine at that time.

A little over an hour later, Crump, holding the boy in his arms, pounded on another neighbor's door yelling that the boy was not breathing. He was limp and unresponsive, the complaint said.

Crump told investigators a couple of different stories about what happened that morning, but never admitted to abusing the toddler, authorities say. He was arrested when he went to the hospital to meet his girlfriend, the boy's mother.

When police searched Crump's vehicle, they found traces of blood on the floor. In a search of the boy's mother's apartment, they found the shirt the boy had been wearing when the neighbor dropped him off with Crump.

The collar was "completely stretched out and the stitching was coming loose," the complaint said. The boy's mother said that when Crump picked her up from work to take her to the hospital, his shirt "had snot all over it" and he took it off and threw it in the trash at a gas station, the document said.

A next-door neighbor told police that between 5 and 6 a.m. Thursday, he had heard a loud, banging noise coming from the apartment where the boy lived. Then he heard a high-pitched scream that sounded like it came from a child. That was followed by more banging noises.

A doctor at Children's Hospital of St. Paul said the boy's injuries constitute "severe trauma, are life-threatening and child abuse is the most likely diagnosis," the complaint said. The injuries likely were inflicted shortly before the boy was rushed to the hospital.

A pediatric neurosurgeon said the boy could have long-term complications, including paralysis or impaired mental abilities.

South St. Paul Police Chief Bill Messerich said Monday that police have not had any previous contact with Crump.