SIOUX FALLS, S.D. (AP) — A Sioux Falls man who could face the death penalty if convicted of killing his infant son has pleaded not guilty. A grand jury last week determined that Dylan Castimore can be charged with first-degree murder in the death of 8-week-old Daxton Castimore. The defendant was originally charged with second-degree murder and manslaughter. Minnehaha County State’s Attorney Daniel Haggar has not decided whether to pursue the death penalty, which became a possibility with the new charge. Should Haggar decline the capital punishment option, Castimore would face a mandatory life sentence An autopsy determined the baby’s death was caused by a skull fracture.