Philadelphia (CNN) -- Playing catch in the yard. Walking in the park. Watching a Phillies or Flyers game. Laughing.
It's the simple things Rob O'Neill said he misses most about his only child, Bailey.
Cupping his chin, O'Neill slowly scans his living room and sighs.
"Honestly, I just miss sitting with him on the couch," said O'Neill, 39. "I won't hear 'Daddy' anymore. That's tough."
O'Neill said his son was punched during a bullying incident at recess at Darby Township School on January 10. He said Bailey, a 6th grader, suffered a fractured nose, a concussion and seizures from the attack. Two weeks after the incident, he was placed in a medically induced coma.
Bailey's parents wanted him to see his 12th birthday. The next day, on Sunday, they took him off life support.
O'Neill said his son told him that one boy pushed him into another boy who allegedly bullied him and punched him. His son didn't want to fight, he said.
"He wanted to walk away and couldn't," he said. "If someone wants to walk away, let them walk away."
O'Neill said the fight occurred in the late morning, and Bailey was sent back to class. However, the boy's mother, Jina Risoldi, wasn't notified until several hours after the incident, he said.
In the days after the altercation, Bailey -- who usually enjoyed skateboarding or playing video games -- started becoming sluggish, experienced mood swings and was otherwise "not himself," O'Neill said.
The Delaware County District Attorney's Office said the case remains an active criminal investigation, and it is working to determine whether the incident -- captured on video surveillance -- was, in fact, bullying or an altercation on the playground.
The district attorney's office is also awaiting autopsy results to determine whether the injuries Bailey received during the incident caused his seizures.
"There was an incident between two 11-year-olds in the schoolyard and certainly there appears an assault that occurred. We will act on that assault at the appropriate time," Jack Whelan, Delaware County District Attorney, told CNN affiliate WPVI.
"But the question really is, did more occur in that schoolyard, did those injuries sustained, were they attributed to the incident in the schoolyard?" Whelan said. "We need that question answered."
O'Neill said he stands by his claim that his son was bullied.
"He told me the story himself. And there's no reason for him to lie about it," he said. "It's in my heart, I know what happened and I would like to see justice."
U.S. Sen. Bob Casey of Pennsylvania, who is working on anti-bullying legislation, told CNN's Soledad O'Brien that he believes bullying today is far more damaging than in years past.
"This is an epidemic, and unless we deal with it, we're going to have all kinds of problems down the road for these people who can't function, can't study, can't do the work they have to do to succeed," Casey said.
The family has received an outpouring of support, including from Baltimore Ravens Ray Rice, who spoke to the family and later took to Facebook to speak out against bullying on behalf of the O'Neill family.
The Super Bowl champion running back wrote in part: "Bailey - my little buddy, I will not let you become just another bully statistic...you are my inspiration and one more angel that will help me continue the fight for kids everywhere. You are going to help me save lives."
The Southeast Delco School District issued a statement Monday offering its condolences to Bailey's family and friends.
"Our school community is deeply saddened by this loss," Superintendent Stephen D. Butz wrote.
"Additional counselors have been made available to assist our students and staff with the emotions around the death of Bailey. The school district continues to work with local authorities in their investigation into the cause of Bailey's death."
A public visitation is scheduled for Friday, a day before his funeral.
O'Neill said he doesn't want Bailey's death to be in vain and started the Battle for Bailey campaign to help raise bullying awareness and connect with others going through similar situations.
"I wasn't Super Dad, but he looked up to me, and I have to be strong for him," he said. "I don't want to see anyone else end up like Bailey."
Although nothing can bring his son back, O'Neill said he is at peace.
"I'm at peace at the fact that he doesn't have the pain anymore, and I feel that he's safe now," he said. "He doesn't have to suffer anymore."