Another repulsive attack. The perpetrator sounds like a strange mix of infantile memes and mass murder. The streaming of it and letting his little online clique know beforehand, it's so modern and disturbing.
This case sounds unusual. She was in a park with her friends while two youths were lurking nearby. The two leave and return 30 minutes later where one stabs her in the back without saying anything. No argument or fight. No motive.