A Marine accused of killing his 3-month-old son shortly after his wife died of childbirth complications pleaded not guilty Monday to murder and child abuse charges.

Lance Cpl. Robert Quiroz, 20, was arrested Nov. 20 on suspicion of killing his son, Roman Quiroz, after officials found the infant unconscious in the family's apartment. The child died at a hospital of blunt force injuries, authorities said.

Quiroz was pulled from his first tour of duty in Iraq in August to attend to his wife, who suffered an aneurysm after Roman was born. When she died, the Marine began raising Roman and the couple's toddler on his own, a responsibility he was not equipped to handle, said his lawyer, Ernest Kinney.

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"I think it's a case of negligence, not murder," Kinney said. "We'll be looking for an acquittal or a ruling of involuntary manslaughter."

Police started a child abuse investigation in October after the baby was hospitalized with a broken arm. The county Department of Children and Family Services gave the child back to Quiroz after three days because staff could not prove the boy had been abused.

The state Department of Social Services is looking into county social workers' handling of the case.

Quiroz was being held at the Fresno County Jail in lieu of $2.3 million bail.

A preliminary hearing was set for Jan. 10.

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