"Oh, my God, I have so many mixed feeling about all of this," the victim's son, Joaquin Rivera Jr., told the Philadelphia Daily News.
Police are probing the death of a 4-month-old who was living at Marine Corps Air Station Miramar.
San Diego police first became aware of the situation on Wednesday at about 7:45 p.m., when they received a report that a child on the military base was not breathing. Law-enforcement officials said the baby's father, a 22-year-old active-duty Marine, began CPR, then the paramedics arrived and brought the infant to Children's Hospital.
Child Abuse Unit detectives were called to the hospital after doctors discovered the infant had unexplained injuries, police said. Their investigation revealed that the baby's injuries were life-threatening, according to officials. Homicide detectives were then called in.
Police said the baby's father, who was caring for the child, was questioned after the initial report was made but was released pending additional investigation.
The child, whose name had not yet been released, died Thursday morning at Children's Hospital. An autopsy has been scheduled for Friday.