The teenager, who had not been named last night, is believed to have tried to hang himself in the cell at Hartlepool police station, although the results of a post-mortem examination conducted yesterday will not be released until today.
The death will be viewed as particularly controversial because juveniles are not supposed to be held in police cells under any circumstances.
The 15-year-old had been arrested on suspicion of burglary and was found unconscious by custody officers at 3.15 pm on Monday. It is understood that officers resuscitated him before paramedics rushed him to Hartlepool General Hospital. He was put on a life support system but died at 11am yesterday morning.
Cleveland Police voluntarily referred the case to the Police Complaints Authority on Tuesday.
Neither the force nor the authority would comment on reports that the youth, understood to be from the Hartlepool area, had used the waistband of his track suit bottoms to try to hang himself. "It is too early to speculate on the cause of death," an authority spokeswoman said.
Tony Williams, the authority member supervising the PCA investigation, has agreed to the appointment of Superintendent Len Ross of Cleveland Constabulary's complaints department, as the investigating officer.
The boy's family have requested anonymity. Supt Ross said: "We are investigating an incident at Hartlepool police station. We are respecting pleas from the boy's family for no publicity and we are speaking to other people who were in the cells."
Roger Ede, secretary to the Law Society's criminal law committee, said the Code of Practice under the 1984 Police and Criminal Evidence Act made it clear that juveniles should not be placed in the cells.
"Most police stations would have a detention room for those juveniles who need to be detained," Mr Ede said. "The rooms are much more spacious and less intimidating than cells and, crucially, nearer the custody officer. But juveniles are sometimes put in cells because there is nowhere else to put them."
Mark Grindrod, juvenile project manager for the Howard League for Penal Reform, said: "If you have juveniles in custody you have to have particular concerns about their vulnerability, because they are particularly volatile and particularly prone to carrying out acts which perhaps they do not fully think through. That's why we have such specific and stringent safeguards about interviewing and detaining juveniles, with onerous responsibilities placed on those - whether in police stations or prisons - who have custody of them."
A juvenile should not be held in a cell before being interviewed and a decision over whether to charge him or her is reached. Once a decision to charge has been made, police can bail the person into the care of social services, or send him or her home, pending a court appearance.
The boy's death follows a series of suicides by juveniles who were being held in prisons.
The Howard League warned warned this week that the prison suicide toll would continue to rise as the jail population spirals.Reuse content