Terrorists often want their goals to be known, because it tells the group they want to manipulate with fear what they are expected to do. That is the reason why terrorist groups publish videos claiming the deed after they, for example, bombed a recruitment centre. They want people to know it was them and threaten everyone going to that place to join police/military. Even if an actor works solo, it helps their goal to go public and also claim there are like minded people.

So I think it's actually reasonable to just ask.