That sounds like a horrible case for carving such an exception. The suspect dumped his gun in a grocery aisle and that
created an immediate threat to public safety? It's not like a pistol in a pile of broccoli is going to get up and start shooting people, unlike a bomb with a timer.
Was the gun a clear threat to public safety, or were the police just feeling too lazy to go search for all the evidence, reaching behind all the cereal boxes and canned goods and creating a terrible mess to cleanup on aisle 3? If a gun in a store is such a dire and immediate threat to public safety, then why are gun stores with whole shelves of them such a safe place for police and the public to hang out?
The current incident would be a much, much better case for establishing such an exception.