Three years ago, a Crown Prosecution Service lawyer dropped a rape case involving an under-age girl which could have left a sex grooming ring undetected for years.
The teenager was arrested outside a takeaway in Heywood in August 2008 for being disruptive.
She alleged one of the workers had groomed and then raped her.
Greater Manchester Police (GMP) investigated Kabeer Hassan and another man, aged 59, but it was nearly a year later when a CPS lawyer decided to drop the case.
According to Nazir Afzal, chief prosecutor for the North West, the lawyer had viewed six hours of video testimony from the girl and also had DNA evidence, but decided "she would not be viewed as a credible witness by a jury".
Hassan and the other man, who cannot be named, have been convicted by a jury at Liverpool Crown Court with seven others, all from Greater Manchester, who groomed young girls for sex by plying them with drink and drugs.
The file of the girl's allegations was one of the first on Mr Afzal's desk when he started his new job in the summer of 2011 and he took "an immediate decision" to prosecute Hassan and the 59-year-old man.
By then GMP's Operation Span, launched in December 2009, was under way investigating allegations from other under-age girls in the Rochdale and Heywood areas relating to the other defendants.
However, Mr Afzal maintains he would have charged both men even if the only evidence available had been that which led to the original case being dropped.
"I took the view that a jury would have found her a credible witness," he said.
"I regret that the wrong decision was made."
Mr Afzal said his decision to prosecute was based on 20 years experience including expertise in rape cases.
The CPS's dropping of the original case led police to stop all investigations, a decision that is now the subject of separate inquiry.
The original lawyer, whose decision was reviewed and backed by a CPS unit manager, has been taken off rape cases and is undergoing retraining.
The way GMP treated the 2008 allegations is at the centre of a managed investigation by the Independent Police Complaints Commission (IPCC).
It was only after a second girl made similar claims in December 2009 that detectives began Operation Span.
Police went on to find more than 40 vulnerable and at risk girls across Rochdale and Heywood subjected to on-street grooming by a network of men, mostly takeaway employees and taxi drivers.
All five girls who were witnesses in the gang's conviction were known to social services at some stage in their lives.
GMP is not commenting directly on the IPCC inquiry, but Assistant Chief Constable Steven Heywood concedes the force has made mistakes.
"We apologise to anyone that has suffered due to any failing on our part, " he said.
"We probably could have done things better.
"We and other agencies are on a journey, we know more about this kind of crime than we did in 2008."