Unfortunately this one actually happened in Florida. Police arrested a guy who, among other things, someone had said was in possession of something that "looked like a pistol with a suppressor." After searching the guy and finding no such weapon the cop put the guy, handcuffed, in the back of his cruiser. As he walked away from the car an acorn fell and hit the roof, at which point the cop started shouting into his radio about shots fired and that he had been hit by gunfire, dove and rolled around a bit (nowhere near any actual cover), then unloaded the entire magazine of his pistol at his cruiser with the suspect locked inside it. Another officer on scene, reacting to the first one yelling that he'd been shot, also fired all of her ammo at the vehicle. None of the shots actually hit the handcuffed guy in the back seat.
A "thorough investigation of the incident" (including body camera footage from both officers involved which is now publicly available online) determined that the noise the first officer thought was a suppressed gunshot was, in fact, an acorn hitting the roof of the police vehicle after falling from the large oak tree it was parked next to. The acorn was still on the roof. Despite his panicked reaction and assertions otherwise it was also determined that he had not been struck by gunfire and that he was certainly the first person present to start shooting. The other officer was cleared of any wrongdoing as she was determined to have had legitimate reason to believe there was a clear and present danger. The first cop, who gave the second one that reason by freaking out over a fucking acorn, was determined to be whatever the official wording is for delusional, unstable, and dangerously incompetent and he resigned. In statements he still insisted after the fact that, while not disputing the findings of the review, he still recalls having heard a gunshot and feeling an impact to his torso.