A two-phase statutory public inquiry into the Southport murders has been formally launched.
Home Secretary Yvette Cooper said the first phase would look at the circumstances around Axel Rudakubana's attack on a Taylor Swift-themed dance class last summer.
It will focus on issues around policing, the criminal justice system and the multiple agencies involved with the attacker who killed three girls - seven-year-old Elsie Stancombe, six-year-old Bebe King and Alice da Silva Aguiar, nine.
It follows the revelation Rudakubana had been referred to the government's Prevent scheme on three occasions, with the cases being closed each time.
The second phase of the inquiry, which will be chaired by retired judge Sir Adrian Fulford, is expected to examine the wider issue of children and young people being drawn into extreme violence.
Ms Cooper said: "The brutal murder of three young girls: Bebe, Elsie and Alice in Southport was an unimaginable tragedy - we owe it to their families, and all those affected on that terrible day to quickly understand what went wrong, answer difficult questions and do everything in our power to prevent something like this from happening again.
"The Southport Inquiry will provide insights into any failings that allowed a young man with a previous history of violence, to commit this horrendous attack."
The home secretary first announced there would be an inquiry into the Southport murders in January, after Rudakubana pleaded guilty to the murders of the three girls.
He also admitted 10 counts of attempted murder and possession of a kitchen knife over the mass stabbing, as well as charges of producing ricin and possessing an al Qaeda training manual found in searches of his home in Banks, Lancashire, in the following days.
Eight other children, aged between seven and 13, along with yoga instructor Leanne Lucas and businessman John Hayes, were injured in the attack, which took place at the Hart Space in the Merseyside town on 29 July.
In the aftermath of the stabbings, misinformation about the attacker - including false claims that he was a 17-year-old asylum seeker who had come to the country by boat - were spread online, sparking riots across England.
This breaking news story is being updated and more details will be published shortly.
Please refresh the page for the fullest version.
You can receive breaking news alerts on a smartphone or tablet via the Sky News app. You can also follow us on WhatsApp and subscribe to our YouTube channel to keep up with the latest news.