Six months after a teenage attacker stabbed three girls to death at a children’s dance class in England, new details about his background have sparked questions about how authorities repeatedly failed to spot the threat he posed.

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.

A British teen pleaded guilty Monday to murdering three girls and attempting to kill 10 other people in what a prosecutor said was a "meticulously planned" stabbing rampage at a Taylor Swift-themed dance class in England last summer.