Three South Wales Police detectives face being struck off after an investigation found they were told Lost Prophets singer Ian Watkins could be a paedophile four years before he arrested.
The Independent Police Complaints Commission (IPCC) has started misconduct proceedings on a detective sergeant and two detective constables after their investigation into the force found members of the public, Crimestoppers, or other police forces had alerted them in 2008 about possible paedophilia.
Watkins, former singer with the rock band Lostprophets, was arrested in 2012 and sentenced at Cardiff Crown Court in December 2013 to 29 years' imprisonment for serious child sexual offences.
An IPCC statement said the detective sergeant has a case to answer for gross misconduct and misconduct. "In the IPCC investigator's view the officer did not take sufficient action to progress enquiries, and contributed to allegations from a main witness being treated as unfounded," it said.
The two detective constables, the statement added, have a case to answer for misconduct, "as they did not undertake all reasonable and practicable lines of enquiry".
IPCC Commissioner for Wales, Jan Williams, said: "Having completed detailed investigations over recent months we have liaised with South Wales Police over our misconduct recommendations. 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. This has been a complex process.
"We aim to issue our fuller findings, including our examination of the wider organisational response of South Wales Police, following the conclusion of the misconduct proceedings currently being arranged by the force."
The IPCC carried out three investigations into how the force responded to reports and intelligence dating back to December 2008 by members of the public, Crimestoppers and other police forces,
The last one, involving the detective sergeant, based in the force's Northern Command Unit, recommended he has a further case to answer for gross misconduct due to his lack of action in response to an allegation against a different suspect that a 15-year-old girl had been raped.
Watkins, 36, from Pontypridd in Wales, admitted charges including the attempted rape of a baby and was jailed alongside two mothers whose children he abused. One woman was jailed for 14 years, the other 17.
During sentencing, Mr Justice Royce said Watkins showed a complete lack of remorse and posed a significant risk to the public. He said: "Those who have appeared in these courts over many years, see here, a large number of horrific cases. This case breaks new ground. Any decent person... will experience shock, revulsion and incredulity."
In response to the IPCC's decison, South Wales Police assistant chief constable Jon Drake said: "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. (Friday 1st July)
"The IPCC has made a number of recommendations both in terms of organisational learning and individual officers. We accept these recommendations and will respond promptly to the investigation and its findings. This will include the progression of misconduct proceedings, to take place in the autumn."