On 29 July 2024, a knifeman entered a Taylor Swift dance class in Southport, murdering three girls and attempting to kill many more.

It is a story with a lot of whys - why did a 17 year old schoolboy murder three little girls and try to kill even more? Why did he target that dance workshop? And why does it seem that no one - not his family, not the police, not social services - could see him for the danger he was?

Anna Youssef speaks to Dr Samantha Walkden, a senior lecturer in forensic psychology at the University of Greater Manchester and a chartered psychologist.