The schoolboy was certified dead on Tuesday night in the intensive-care unit of Sheffield Children's Hospital where he had been on a life-support machine for 12 days. He had not recovered consciousness since being found. His parents, Patricia and Grenville, agreed to his organs being donated for transplant.
A spokesman for South Yorkshire police said that the death was being treated as suspicious, but not as murder. It was being investigated 'with the thoroughness of a murder inquiry'.
John was found outside the Rowena Infant School near his home in Conisbrough, South Yorkshire, on 3 June by his brother, Lee, 13. Neighbours tried to revive him but it took electric shock treatment by ambulance paramedics to restart his heart.
Dr John Clark, the Home Office pathologist who carried out the post- mortem examination yesterday, said that the cause of death was brain damage due to hanging.
Detective Superintendent John Hope, who was heading a team of 60 officers investigating John's death, said the chances of it being an accident looked 'increasingly unlikely'. He said that it was more likely to have been a schoolboy prank which went wrong, or 'something more sinister'.
He said: 'It is extremely tragic and our hearts go out to John's family. We are doing all we can to try and get to the bottom of this. We are treating the death as suspicious . . . I can't say he was murdered because I simply don't know. We have had a lot of help already from members of the public but we are still wanting to trace anyone in the area between 4pm and 4.25pm on Friday 3 June.'
The owner of the plaited-rope dog lead, who was traced soon after the tragedy, has told detectives that it had disappeared two days before the incident.
Det Supt Hope said he was keen to question a cyclist seen in the area. 'He has not come forward and may not have done because he is frightened. He may be totally innocent - but he may have vital information to give us.'
The cyclist is described as about 17 and well-built. He wore a dark, shiny zip- up jacket and jeans, and rode a white mountain bike with green lettering.