Most specific stuff I have seen. https://twitter.com/mrwilltolive/status/981260734305918978?s...
It is probably too soon to get reliable information.
[1] https://twitter.com/etharkamal/status/981264092899037185
The Breaking News Consumer's Handbook: Active Shooter Edition
For example at Columbine one of the shooters removed their trenchcoat, which when talking to victims briefly gave the impression of a 3rd shooter.
Good luck YouTube staff, hang in there.