So very sad, RIP Brianna. I hope these convictions will help Brianna's family a little.
I do think the online world and seemingly unfettered access to the internet by these children is a really important factor and we need to remember that although the online safety bill has been passed and hopefully will make things better for children online, there are still some criticisms about how far it has gone from bereaved parents https://www.bbc.co.uk/news/uk-politics-67714572
I'm really disappointed that in the discussion about the online safety bill there was very often conflation between adults and children. There is an argument that adult free speech online should not be restricted but children are not developmentally able to understand or put into context a lot of the worse content on the internet and they do need to be safeguarded and until recently have not been at all on the internet.
What these children did was horrific and maybe they are psychopaths but there has been a huge safeguarding failure of Brianna yes, but also of these children. They should not have been able to access the materials they did online at their age.