An autopsy conducted on the body of an 18-month-old Dakota County boy who died last week found his brain and body battered, authorities said Monday.

Prosecutors will decide by noon Wednesday whether to charge Nicholas Miller's 22-year-old stepfather in his death. This morning a Dakota judge granted prosecutors a 24-hour extension on the deadline under which they'd have to file charges.

A close relative said Monday that the stepfather's arrest lends credence to claims Nicholas' 6-year-old stepsister made to at least one family member that her father had been beating the little boy. The stepsister was among those providing information to Dakota County sheriff's investigators that led to her father's arrest Saturday, relatives said.

The suspect is in the Dakota County jail in Hastings on suspicion of second-degree murder.

On Monday, Dakota County sheriff's investigators were tight-lipped about what they were told by witnesses and family members, including the suspect's young daughter.

Chief Deputy Dave Bellows said his department was notified last week by the Pierce County (Wis.) sheriff about a child's suspicious death. An investigation determined that the injuries occurred in Dakota County before the 18-month-old was taken to Durand, Wis., where he died June 23.

The child often stayed at a dairy farm in Greenvale Township near Northfield, Minn., with his 18-year-old mother, Melissa Miller, and the stepfather, along with her parents. Melissa Miller's grandparents lived in an adjacent farmhouse.

"He was a good little fellow," Nicholas' great-grandfather, Herman Ohmann, said.

Nicholas' autopsy by the Ramsey County medical examiner's office found multiple recent injuries, including damage to his brain. Earlier injuries that had healed also were found, Bellows said.

Ohmann said injuries to the boy appeared after his granddaughter married the stepfather in November.

"Things started showing up that we were all questioning," Herman Ohmann said.

The family once took Nicholas to the doctor with a broken collarbone, Ohmann said. "Well, then, not too long, and doggone, he had another broken collarbone," he said.

The stepfather's daughter from another relationship didn't live on the farm but occasionally visited, Ohmann said. During those visits, she told at least one family member that her father was beating Nicholas, he said.

Ohmann said the girl, who lives in Red Wing, Minn., told her grandmother on the farm, Debbie Ohmann, that her father was hurting Nicholas. But the grandmother "never took it to heart," he said.

Ohmann said that as far as he knows, nobody called police about the 6-year-old's claims or about the injuries they observed on the boy.

When questioned by family members, the stepfather tried to blame the child's biological father and his side of the family for any injuries to Nicholas, Ohmann said.

A supervisor with the Dakota County's child protection unit said information about whether the unit had received any reports of suspected abuse of the toddler cannot be publicly disclosed.

The family had provided a home for Melissa Miller and her husband but grew disillusioned with him, Ohmann said. "We tried to get him a job, get him going, get him on his feet, but he would never get up in the mornings," he said. "He wouldn't do anything."

Ohmann said the couple, with Nicholas and another child, their newborn, were at the farm one or two nights a week. "Where they were all staying, we really didn't know," he said.

Herman Ohmann said he became enraged when he learned what happened to his great-grandson.

"Good God, that little boy," Ohmann said. "He didn't have no future."

Joy Powell • 952-882-9017