Three detectives who received complaints about paedophile rocker Ian Watkins four years before his arrest will face disciplinary proceedings, a police watchdog has said.
Former Lostprophets frontman Watkins is serving a a 35-year sentence after admitting a string of sex offences – including the attempted rape of a fan's baby.
The disgraced singer was arrested in 2012 and jailed the following year.
However, the Independent Police Complaints Commission (IPCC) said South Wales Police was given information about Watkins back in 2008.
Following a detailed probe into the Welsh force, the IPCC has said there are cases to answer against the three officers – one detective sergeant and two detective constables.
A spokesman said: "The IPCC investigator recommended that a detective sergeant has a case to answer for gross misconduct ... (after) the officer did not take sufficient action to progress inquiries.
"The IPCC investigator was also of the view that two detective constables have a case to answer for misconduct, as they did not undertake all reasonable and practicable lines of inquiry."
Watchdog officials added that they have also recommended a further case to answer for gross misconduct against the detective sergeant's "lack of action" about reports that a 15-year-old girl was raped.
The allegations concerning Watkins and the teenager did not feature in his prosecution.
However, a court was told about Watkins's fantasies with underage girls as well as a disturbing encounter with a teenage fan.
Watkins had originally denied any wrongdoing - claiming he had been "framed" by jealous groupies.
However, he changed his plea just moments before his trial was due to start and admitted 13 child sex offences.
Cardiff Crown Court judge Mr Justice Royce handed the shamed rocker a 29-year prison term - with a further six years on licence.
Watkins later launched an appeal against the length of his sentence, but it was dismissed by a panel of judges.
Once the criminal case against Watkins finished, the IPCC began its inquiry.
IPCC Commissioner for Wales Jan Williams described the watchdog's investigation as "complex".
She added: "We probed a substantial number of reports and allegations relating to Ian Watkins made over a four-year period to establish exactly who knew what and when, and how police officers responded."
South Wales Police Assistant Chief Constable Jon Drake said it accepted the IPCC's recommendations and the misconduct proceedings will take place in the autumn.
He added: "In 2012, South Wales Police initiated its own review into the sequence of events prior to the arrest of Ian Watkins.
"We identified that there were issues of concern and voluntarily referred the matter to the Independent Police Complaints Commission, which has resulted in the statement today."
Mr Drake added that the force takes the issue of protecting vulnerable people very seriously.
He said: "We now have dedicated staff dealing with child protection issues and working closely with our partner agencies.
"We know it is difficult taking that first step in reporting child abuse and that people coming forward need support, but we would urge anyone with concerns about a child or young person to get in touch with us immediately."
The IPCC is expected to issue its "fuller findings" on the Watkins case in the coming months.
NSPCC Cymru/Wales voiced concern about the IPCC's findings.
A spokesman for the children's charity said: "Serious questions have long been raised about how the police investigations into Watkins's abuse of children were handled from the moment allegations were made.
"It is of grave concern that the IPCC believes claims of abuse were not properly investigated and that lines of inquiry were not pursued which could have brought Watkins to justice earlier.
"We hope that the misconduct proceedings are concluded swiftly so the IPCC's full findings into how police investigated Watkins's abhorrent crimes can be made public.
"It's an incredibly difficult step to report child abuse so it's imperative that when people do speak out, they have the upmost confidence that what they are reporting will be acted upon immediately."