Merkle’s fault.
5.56mm
Looking at one video, it would appear that the terrorist is filming the original attack. Film starts before the shooting begins - victims flee from the source of the first gunfire - run right into the second gunman. I’m not there, I have no info but the film, but seems clear at least 3 involved here.
Herding - the victims are herded purposefully in the direction of the second shooter IMO. Didn’t they do this in Turkey as well?