A relation of a person involved in that attack has approached me with information regarding what happened. There is a vigilante group operating here, targeting "known pedophiles". The reason this person approached me is because she has grown concerned about the activities of this group, following a recent violent attack on another individual. This person's information is that this group includes an active member of the Indianapolis Metropolitan Police Department, and that the group has misused police resources to obtain information in furtherance of their color of law activities.

...and their membership also includes the prosecutor's office, I notice.

Anyways... name of the group? Known symbols and gang identifiers? Organizational structure... disorganized, classic anarchistic, single-group paramilitary, cell-based paramilitary... ?

As you have noted, there is a vacum in the maintenance of order. Nature abhors a vacum.