As I recall, the issue is technically about search warrants. About twenty or so years ago in Michigan- building fire, the fire department extinguishes the fire and leaves. Several days later arson investigators go back to the scene and find incriminating evidence implicating the owner. He's convicted, and on appeal, the conviction is subsequently overturned. The basis of the reversal involves illegally obtained evidence.
The fire department does not require a search warrant to enter a building in an emergency, but once they leave, they do. So, until the investigation is complete, they have to maintain a presence.