I don’t think the Federals have to classify it as a ‘terror event’ at all. They, being the all powerful Federal Government can call it what ever they want, including a ‘civil rights’ violation or some violation of the Food and Drug act(s).
If they want to take over the investigation - leaving the local police totally out of the case - they have to classify it as a terror event, according to the article. As long as they don’t classify it as a terror event, the local police are still involved in investigating the case and can say what they please about it, as long as they are willing to tell Eric Holder to go suck a lemon when he tells them to say it’s “workplace violence”.