Assume for a moment that a jury finds the state of Florida's case for second degree murder unconvincing beyond a reasonable doubt, refuses to compromise to a lower charge, and frees George Zimmerman, thus setting off riots.
Is he then free for good, under the Constitution's ban on double jeopardy?
Of course not. As seen in the two trials of the cops who whomped Rodney King, the government gets two shots at defendants whose unsatisfactory verdicts cause black riots.
Of course, in the Rodney King trials, the first one was a state trial and the second one a federal trial. As everybody knows, when it comes to Bill of Rights protections, state governments and federal governments don't have anything to do with each other in the slightest. That's why the states can do anything they want regarding civil rights, such as having an established state church. You see, Constitutional rights only apply to the Federal government.
Oh, wait ... that's how it was in 1790, but that got changed a long, long time ago. Well, never mind about that ...
Okay, the real reason the LAPD cops weren't protected by the 5th Amendment's prohibition on double jeopardy is that their two trials were on utterly separate charges. The first trial was on charges of whomping Rodney King and the second trial was on charges of violating Rodney King's civil rights by whomping him: totally different!
Also, you might think that the second trial was inherently likely to be biased since the jurors were under vast pressure to convict so that Los Angeles wouldn't be burned down again by drunken mobs. How can you have a fair trial with a vengeful horde standing in the wings ready to loot, rape, and pillage if they don't like the verdict?
I think, however, you'll find that you've just answered your own question.
Seriously, the most interesting thing I saw about the second Rodney King trial, in which two officers were acquitted and two convicted, was an interview with three of the jurors soon afterwards. I believe it was in the New York Times, but I've never been able to find it online. At the very end of the interview, tossed in as aside, was the stunning revelation by the three jurors that they had only voted to convict based on the last of the 60 or so blows the videotape showed landing on King. They had spent a large amount of time studying the full videotape (not the truncated part shown on TV) in slow motion and had concluded that only the very last of all the blows could be seen beyond a reasonable doubt as unnecessary to subduing the large and energetic King.
My jaw fell about six inches reading this, but as usual with most things that interest me, this fact seems to have disappeared down the memory hole without leaving a ripple in the Narrative. So, maybe I'm just imagining it all ...
My overall opinion of the Rodney King case is what I've always told my sons when giving them "The Talk:" if you make the cops chase you at 100 mph, you get their adrenaline up. And you really don't want to do that because they will likely do very bad things to you when they finally catch you because they will be so worked up they will have a hard time controlling themselves. It's like the end of a fox hunt in England. The hounds don't carefully eat the fox after they finally catch it, they rip it to shreds because the dogs are so overwhelmed with adrenaline.
Moreover, Rodney himself had plenty of adrenaline flowing, too, so he put up a helluva fight. (His friend in the front seat calmly stayed in the car and was untouched.)
Something I've noticed about myself is that I'm the opposite of most people in that I tend to find deciding upon the morality of specific, idiosyncratic cases unappealing. It looks like to me that the cases that most get people worked up over who is the good guy and who is the bad guy tend to be the cases that are most arguable. I look at the Rodney King story and say, wow, that's not very good, how can we more often avoid that kind of thing from now on?
Most folks' turns of mind are judgmental, retrospective, and moralistic. My turn of mind is probabilistic, future-oriented, and technocratic. So, for example, the Rodney King case seems to have been an example of the bad consequences of a 100 mph chase. But you can't let criminals escape just by driving away fast. So, the best thing to do is to discourage criminals from, in the first place, trying to get away by driving 100 mph. How? By making sure they almost always get caught. And, indeed, it appears the LAPD actually has managed to get better at tracking fugitives with helicopters, so that they are now less likely to try it.
Here's another technocratic idea: as we know, whomping hell out of Rodney King with batons came about in part because LAPD officers weren't allowed anymore to use the windpipe-closing chokehold that they had formerly been taught to use on out-of-control arrestees. The problem was that cops would periodically choke people to death, especially black guys who had really pissed them off. Was this because cops were seized by an irrational, uncaused hatred of black guys or because black guys tend more often to do things that really piss cops off? The first answer is the only socially acceptable one.
So, the two dozen cops trying to apprehend Rodney King saw themselves as having not much alternative to bouncing truncheons off Rodney until he decided to come quietly. (Plus, they'd been chasing him at 100 mph, so whomping him just seemed like a good idea at the time.)
To me, it seemed like there has to be some kind of technological improvement that was better than either whomping or wading in and getting a chokehold. And, indeed, we've seen police forces equipping cops with stand-off weapons such as tasers and pepper spray.
P.S. Commenter gwern found an article from the LA Times, not the NY Times as I recalled. (I was a subscriber to the NY Times in Chicago at the time, but I was vacationing at my parents' house in LA at the time of the verdict in the second trial.)
Jurors also played and replayed the best evidence in the case—the videotape of the beating that had been taken by an amateur and enhanced by the FBI.
"We went through it frame by frame, slow-motion, fast-motion, God I don't know how many times we watched that thing," Juror No. 9 said.
The tape, made by a bystander, could not answer all their questions. It was blurry at one crucial moment after King was struck and fell to the ground. Some jurors said they could see Powell using his baton to bash the fallen King in the head. But others had difficulty seeing head blows, even when the tape was viewed frame by frame.
All could see a powerful blow that Powell later landed across King's chest. King was on the ground at the time, on his back.
"That chest blow was unreasonable and we felt it was not to effect an arrest but just to hurt the guy," No. 9 said. "That convinced about a third of us."
Powell's laughter while making a radio call to request an ambulance for King also contributed to jurors' impressions that he had acted callously. But the panel stopped short of taking a vote.
So, to the extent that this is the article I remembered, it doesn't say that it was the last blow that led to the conviction, just that there was one blow that was seen by a significant fraction of the jury as unjustified beyond a reasonable doubt. But, in any case, that's awfully different from The Narrative.