National Crime Agency chief's apology to children at risk of abuse
The head of the National Crime Agency says he accepts children could have been at risk, because it was sitting on data about possible paedophiles.
The files held by the agency included details of a Cardiff deputy head teacher who set up cameras to film children.
It emerged information on Williams, who was arrested in January, had been available for two years.
Giving evidence to MPs, the head of the National Crime Agency (NCA), Keith Bristow, apologised to children who could have been put in danger.
He told members of the Home Affairs Select Committee: "Sitting on data for a period of time, between July 2012 and November 2013, that could have led to children being protected or safeguarded seems to me - whether its systemic or down to individuals - that is not in the spirit of what we stand for.
"I'm sorry if that has led to harm to children or exposing them to risk."
The Independent Police Complaints Commission is currently examining the NCA response to the matter, which was a response to a police operation in Canada called Project Spade.
Giving evidence to MPs on Tuesday, Mr Bristow admitted: "I'm disappointed we've had to refer ourselves to the Independent Police Complaints Commission, and more that we may not have managed the risk to a group of children as much as we would have liked."
Project Spade resulted in the arrest of Toronto film-maker Brian Way in 2011 for allegedly making and distributing images of child sex abuse.
Canadian police then alerted law enforcement agencies in 50 countries to people - including Williams - who had used Way's website to buy images.
The information was passed to the UK's Child Exploitation and Online Protection Centre (Ceop) in April 2012.
But it was November 2013 before those details on 2,345 UK suspects were passed onto local police forces.
Mr Bristow told MPs: "I wish we had known sooner, but we took immediate actions as soon as we became aware."
South Wales Police have said they acted in the case of Williams once the intelligence was received.