A British teenager on Monday pleaded guilty to charges of murdering three young girls in a knife attack in northern England in July, a crime that horrified the nation and was followed by days of nationwide rioting.

Home Secretary Yvette Cooper said agencies "failed to identify the terrible risk and danger to others" that Axel Rudakubana posed - and answers are needed about why.

Axel Rudakubana on Monday admitted committing the deadly attack last July. Officials later said he had been referred to a government counterterrorism program three times before his rampage.