No, they caught him on the spot. At first the cops did not register that he was actually stabbing people, so they did what they had been instructed to do: use the slightest opportunity to attack and arrest the "far right wing provocateurs" (that would be the people who were legally and peacefully assembled there exercising their freedom of speech and association).

They wouldn't have given a fuck about the attacker if he had not been armed and actually wounding people, let alone a cop. But in this case, they *had to* stop him.