Detective Inspector Aaron Pascoe said members of the community had provided helpful information during the investigation, which would be referred to the Coroner.
The circumstances of the death, including whether it was a suspected suicide or an accidental death, was a matter for the Coroner to consider, a police spokeswoman said.
O'Neill was released from prison just two months before his death. He had been jailed for injuring, intentional damage, possessing a firearm and unlawfully getting into a motor vehicle.
The 34-year-old told the Parole Board at his final hearing that his gang connections kept him safe in prison but he had plans to "better himself" when he was released, and wanted to get a qualification.