In this case this shooting event will consume the hours and minutes of the news cycle, create yet more furvor for gun control and generally cause chaos.
You can't go on the offensive if you are constantly defending a position and or putting out fires.
You could however go on the offensive and change the narrative if your action was on a grand enough scale to usurp the narrative. A high profile arrest would do that, however, risking the success of the case that follows the arrest is not worth going on the offensive with it.