Based on the nature of the attack and what we know about him so far, I’d be astonished if it doesn’t come out that he was involved in incel spaces online.
Isolated, possibly autistic young men attacking girls and women have usually spent too much time in spaces that dehumanise women and blame us for not ‘giving them sex’. Sadly, little girls dancing in a way incels deem ‘sexual’ might have been a trigger (I feel sick typing that, but it’s true based on my experience of these types of people)
(i say this as an autistic person - it’s no excuse, there’s just a certain type of misogynist entitled male who struggles to get a date because of autism-related lack of skills and decides that’s somehow the fault of women)