Whelan said an autopsy by Edwin Lieberman of the Philadelphia Medical Examiner's Office revealed "no physical finding of trauma or evidence that trauma played a role" in the boy's death on March 3 at Children's Hospital of Philadelphia. He was 12.
The boy's father, Robert O'Neill, who has said his son was bullied and beaten at the Darby Township School on Jan. 10, declined to comment.
Whelan said Robert O'Neill was "disappointed" in the outcome of the investigation, but he added that he was in no position to judge whether any bullying was involved.
The fight was egged on by an "instigator" who told a companion that Bailey wanted to fight him, Whelan said. In the school yard, Bailey and the other boys were pushed toward each other by two unidentified boys.
Whelan said that during the fight, two to four punches landed on Bailey's face and that Bailey did not fight back.
He said that Bailey's head did not hit the ground and that he went down on one or both knees. He said the fight lasted about 30 seconds. Bailey O'Neill went to the school nurse's office and was out of school the following day, a Friday.
Two weeks later, he was hospitalized and later placed in a medically induced coma.
Robert O'Neill said he heard that about a week before the fight his son had bullying problems with the boy who allegedly punched him. He said other parents had said their children had had bullying problems at the school.
NFL player Ray Rice of the Baltimore Ravens said he had been in touch with Bailey's family and vowed to combat bullying.
"Whether you conclude this is bullying or not bullying, I'm not here to address," Whelan said.
While "the evidence indicates that there is no trauma" from the fight that might have contributed to the boy's death, Whelan said, "Bailey's mom and dad suffered greatly."
Contact Kathy Boccella at firstname.lastname@example.org, 610-313-8232 or follow @kathyboccella on Twitter