For the record, from an emergency services point of view they dont just tag along everytime the fire brigade turns up, its a standard response SOP to have police in attendance (at discretion of the fire agency's incident controller), usually to deal with crap the firies dont want to have to deal with when they get there(control of bystanders, traffic etc etc) The most investigation police should be doing is noting of surroundings and maintaining a sterile accident scene to preserve evidence for the ATSB investigation.
Over-zealous cops probably want to take control of the situation (save the day) and question witnesses and the pilot, but are going beyond their authority in doing so.
...disco