Fresh evidence has emerged that authorities in Rotherham were warned about child sexual exploitation in 2003 and again in 2006.
Police and council officials took no action despite being told organised gangs were grooming and abusing girls.
Ex-South Yorkshire Police drugs analyst Angie Heal said she "cannot fathom" why her reports did not lead to action.
Last year, an inquiry found 1,400 children were abused by gangs of men, mainly of Pakistani origin.
The abuse happened between 1997 and 2013.
In the first report, released under a Freedom of Information request by The Sheffield Star, Dr Heal warned in 2003 there was no room for complacency over the issue.
However, in a follow-up report three years later, she again detailed the problem saying the situation in Rotherham was established and very serious.
'No holds barred'
The reports, which also highlighted child sexual exploitation in Sheffield, said girls in Rotherham were being abused by gangs also involved in drug dealing and violence.
The findings came about after Dr Heal was appointed in her capacity as a strategic drugs analyst to carry out research on drug use, drug dealing and related problems in the county from 2002 to 2006.
The 2014 Jay report, which uncovered the scale of child sexual exploitation in Rotherham, makes reference to Dr Heal's 2003 report being contained in an information pack, which was presented to Rotherham Council in November 2004.
It also states both the 2003 and 2006 reports were sent to high ranking offices and other agencies including South Yorkshire Police's district commander and chief superintendents.
Rotherham Council, which is now run by government appointed commissioners, said it had been "unable to find any reference to the documents being formally considered" by the authority.
"I just cannot fathom why no action, no concerted action, was taken," said Dr Heal, who has since left the South Yorkshire force.
"There didn't seem to be a co-ordinated response from senior police officers to this really, really serious crime."
Speaking to the Victoria Derbyshire programme, one abuse victim said the lack of intervention was "sickening".
"They knew what was happening yet they still let myself and many others suffer and be raped on a daily basis."
"Even 13 years on, I've been fighting constantly just for answers."
Findings 'widely known'
South Yorkshire Police and Crime Commissioner Alan Billings said agencies knew about Dr Heal's reports at the time but were focusing on other issues.
"The reports are utterly shocking. When you read them there's no holds barred," he said.
"They went not only to police and local government but to safeguarding boards and the national government. It was widely known what she said.
"I think there are more people that have questions to answer than the police. The only sense I can make of it is that at that time, police were prioritising other things like burglary and car theft. I don't think anyone understood what grooming was."
In a statement, South Yorkshire Police admitted to past failings and pointed to an ongoing investigation by the Independent Police Complaints Commission into misconduct issues.
It said it had made "significant progress" in tackling child sexual exploitation but understood more "needs to be done".
"Anyone that understood the issues of child sexual exploitation and abuse would have thought there was a moral duty to act, let alone a legal duty," Dr Heal added.
"It meant that a significant number, over 1,400, continued to be abused, exploited, raped, their families devastated by what happened.
"It makes me really angry and very upset that it was allowed to continue."