I suspect they are unsure of whether they have caught all the protagonists.
I think it's for the best. I really don't think they should take the risk that they may not have arrested all of the individuals involved. It's a very frightening situation, for now and for the future. It's almost impossible to police the whole length of a stage race to prevent crazies from blowing shoot up. Mass spectator events are so vulnerable to attack.
We can help by accepting the decision of the organizers and be extra vigilant and report any concerns if we see them whilst spectating.