No police officer will be disciplined over a force-wide failure to tackle the sexual abuse of teenage girls in Rochdale, according to a report by Greater Manchester police (GMP).

The force looked at the conduct of 13 officers between 2008 and 2010, but served notices of misconduct on only seven. Ultimately only one officer, an inspector, was found to have warranted disciplinary action but he was able to retire without any sanction being taken against him. The remaining six officers were given “words of advice” by superiors.

GMP took four years to complete the investigation under the supervision of the Independent Police Complaints Commission (IPCC). The officer who retired had been in a supervisory role in 2008 when Girl A, the teenager at the heart of the landmark 2012 trial of nine paedophiles, made her allegations of abuse. He had been in the force for 30 years.

A second officer failed to serve an abduction notice on Shabir Ahmed, the leader of the gang who preyed on girls visiting two takeaways in Heywood. A third was criticised for yawning while interviewing Girl A about her allegations.

The assistant chief constable of Greater Manchester police, Dawn Copley, acknowledged “mistakes were made and victims let down”. She laid some of the blame at the force’s focus in 2008–10 on targeting such crimes as burglary.

There was also a widespread lack of understanding about the complexities of child sexual exploitation. But she insisted that lessons had been learned in the aftermath of the failings.

Nine men from Rochdale and Oldham were found guilty of offences that included rape and conspiracy to engage in sexual activity with a child. Eight were of Pakistani origin, the other from Afghanistan. The court heard the group had plied five victims with drink and drugs and “passed them around” for sex.

Girl A reacted with fury at the report. “I’m fuming,” she said. “It’s taken them four years and it reads like a whitewash. These policemen have done wrong and yet none of them has been named and the one they wanted to discipline has been able to retire. It just seems very, very convenient.”

She added: “At one point in the report they say I didn’t want to proceed, but that’s not true. I never said that. Overall I’m disgusted. They and Rochdale social services let me down, and they’re letting me down now.”

Copley also expressed regret at the delays in revealing the contents of a report that was twice rejected by the IPCC. It was due to be published last summer, but was withdrawn at the last minute after Rochdale council expressed concerns that victims might be identified. The resulting redaction took 10 months to complete.

She said the force had a file “ready to go” in relation to the misconduct allegation. “The report went to the IPCC in October 2013. They had it for about six months before they responded to say it had been signed off. The officer retired in that period. There was no reluctance on the part of GMP to have gone forward with those proceedings. We could not prevent someone from retiring. There is no power to do that”.

She went on: “Officers have to account for their actions, and if they have misconducted themselves professionally then they ought to face misconduct proceedings. Very often, if they’ve misconducted themselves, it’s because they’ve acted in bad faith or have been willingly neglectful.

“But if they’ve made genuine mistakes, if they’ve simply misunderstood what they’ve been dealing with, that is not necessarily misconduct. It is probably more of a performance issue, and the organisation has already acknowledged through the serious case review that organisationally GMP did not recognise this (crime) for what it was.”

The investigation concluded that the inspector, identified only as Officer 6, had “a compelling case to answer” for misconduct. He had failed to produce any meaningful investigative strategy, failed t0 keep records of strategy meetings, and chosen not to properly update colleagues on “the scale of the harm to victims and the complexity of the investigation”.

He claimed to have been carrying a large workload, but this was “unacceptable”. His actions demonstrated “a particularly poor victim focus”.

In conclusion, Officer 6 would have been required to attend a formal misconduct process had he not lawfully retired during the investigation at the conclusion of his 30 years’ service.

ACC Copley acknowledged “the huge public interest” in the report. But while both she and two colleagues from GMP’s professional standards branch attended a media briefing, they refused to do interviews on air. The force had also kept the release of the report a closely guarded secret, with victims and journalists only allowed copies two hours before the briefing. The force appeared to try to shift blame for some of the failings onto the Crown Prosecution Service (CPS). It was the CPS, it said, who had wrongly judged Girl A to be an unreliable witness. Its lawyers had also dismissed forensic evidence linking Ahmed to underwear worn by her.

But in the briefing ACC Copley agreed that the force – whose detectives had found the teenager to be “an excellent witness” – could have contested the CPS decision. Four years after the original investigation was abandoned Girl A became the pivotal witness in the landmark trial at Liverpool Crown Court.