Paedophile rock star Ian Watkins could have been caught four years earlier had police properly investigated warnings about his behaviour, a damning report by the Independent Police Complaints Commission (IPCC) found.
Between 2008 and 2012, the IPCC said officers from South Wales Police failed to act on reports about the Lostprophets singer from six different people.
On one occasion, a simple check of Watkins' ex-girlfriend's phone when she made a complaint about his paedophilia would have uncovered a message explicitly revealing his wish to have sex with children.
Joanne Mjadzelics' phone was not checked because her complaint was deemed "malicious", the police watchdog said.
A text message sent to her by the singer, and which was on her phone, read: "WISHLIST RAPE A 12 YR OLD F--- TWO UNDERAGE TWINS."
Several other individuals also came forward, some through Crimestoppers, with disturbing information about Watkins' behaviour.
But none of the eight reports or three intelligence logs about Watkins' alleged drug use, possession of indecent images of children, and sexual interest in children led to Watkins being arrested or questioned in those four years.
The Lostprophets frontman, whose former band sold 3.5m albums, was eventually only arrested in 2012 following a drugs raid at his home in Pontypridd, south Wales, during which officers uncovered a stash of child abuse material on electronic devices.
He was jailed for 35 years in December 2013 after admitting a string of child sex offences, including the attempted rape of a baby.
The IPCC said its report "raised the most disturbing concerns about the way in which reports of Ian Watkins' sickening child abuse were handled".
It said there was no evidence to show there was a lack of police action because of Watkins' celebrity status. Instead, it was officers' assessments of Mjadzelics as lacking credibility that meant adequate steps were not followed.
Jan Williams, IPCC Commissioner for Wales, said: "In my view, all the reports made were subject to a biased response, whether this was conscious or unconscious. Some were conflated with reports made by Ms Mjadzelics and were thus dismissed as lacking credibility.
"All those involved in responding accepted the initial sceptical view of Ms Mjadzelics' reports, demonstrating a lack of open-mindedness and professional curiosity. This continued until 'the right type of complainant came along'.
"Police officers will rarely encounter a perfect witness; it is vital that officers ensure they remain open-minded and pursue all appropriate lines of enquiry to establish whether there is any independent corroboration for the allegations being made. This case demonstrates the risks inherent in failing to explore investigative opportunities to the fullest in such circumstances."
Williams said the decision-making on the reports involved a small number of officers but that there were also "weaknesses" in how South Wales Police dealt with allegations of child abuse generally.
This included poor record keeping, poor handling of intelligence and a lack of rigour in progressing investigations.
South Wales Police has apologised and accepted the IPCC findings. It acknowledged it "failed to listen and properly investigate information about Watkins offending behaviour."
The police force agreed with the IPCC that one of its officers had a case to answer for gross misconduct, and two others had a case to answer for misconduct.
An NSPCC spokesperson said the IPCC report should be a "wake-up call" for all those implicated.
"That a simple unchecked mobile phone could have helped to prevent further abuse by Watkins is unthinkable, and is just one cause for significant concern among this catalogue of basic failures," they said.
"While Watkins is now thankfully behind bars where he belongs, and improvements have already been made by South Wales Police, it's clear that very serious mistakes were made in handling multiple early allegations and this report's recommendations must be adopted swiftly."