Someone saw what happened. The police report states he was struck in the head.
A hostile crowd rabidly supporting the murder of Jews? Motive.
Those protecting the murderer are accomplices and should be charged as such.
You would expect those people to do ugly things.
Someone no doubt videoed what happened. I read that he got conked on the head with a bullhorn. If that is true and a witness or two confirms it, that would seem to limit the number of people that might be the killer.