A first-year law student asked me about the relationship of criminal liability and civil liability, and I thought it might be worth discussing more broadly. Let me begin with one part of the relationship: When an act can lead both to criminal and civil liability, how does a judgment in one system affect the possibility of a judgment in another?
1. It's certainly possible to be held liable both criminally and civilly, if your conduct is both a crime and a tort (or otherwise civilly actionable). The Double Jeopardy Clause provides that "nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb," but that refers only to criminal jeopardy, not civil jeopardy. (There is something of an academic debate about whether the Clause was originally understood as covering crimes generally, as the Court has held, or only very serious ones, but I don't know of any indication that the Clause has ever been understood as applying beyond crimes. Note also that the Double Jeopardy Clause doesn't bar prosecutions by multiple sovereigns, such as the state government and the federal government, but that's a separate matter.)
Thus, a rapist could be prosecuted for rape and sued civilly (likely under the tort of battery). In practice, this doesn't often happen, since most criminal defendants have little money, especially after they're done with the criminal litigation; but it certainly happens sometimes.
2. If you get criminally convicted, then this conviction will usually make a civil plaintiff's case against you much easier. Under the doctrine of "collateral estoppel" (sometimes called "issue preclusion"), if a fact has been decided against a party in one judicial proceeding, then that fact is generally binding against the same party in future proceedings (with an important limitation that I'll mention below) even in other jurisdictions and other court systems.
So if a jury -- or, in a bench trial, a judge -- has found beyond a reasonable doubt that you're guilty of committing certain acts, then that's binding against you in a future civil case based on the same acts. The plaintiff might still have to prove other elements required by the tort (e.g., the amount of damages), but whatever facts were necessarily found in the earlier criminal trial don't have to be proven again in the civil trial. If O.J. Simpson had been convicted of intentionally killing Ron Goldman, Fred Goldman wouldn't have had to prove in a civil case that Simpson indeed intentionally killed Ron Goldman; he could just take advantage of the earlier criminal verdict against Simpson.
3. What if you get acquitted, and still get sued (which is what happened with O.J. Simpson)? You can't take advantage of the criminal verdict in the civil case, for two reasons. First, the criminal verdict simply shows that there was at least reasonable doubt about whether you were guilty. That doesn't stop the plaintiff from proving your guilt by a preponderance of the evidence (the standard usually required for civil liability) or even by clear and convincing evidence (the standard generally required for punitive damages in civil cases).
To give an oversimplified mathematical model, say that there's evidence that shows an 85% chance that you were guilty, and say that proof beyond a reasonable doubt requires a 95% chance, proof by clear and convincing evidence requires a 75% chance, and proof by a preponderance of the evidence requires only 51%. In that situation, an acquittal simply means that there isn't a 95% chance that you were guilty; that's quite consistent with there being a 51% or 75% chance that you were guilty (and in the hypothetical, both those thresholds are satisfied).
There's also a second reason why the defendant's criminal acquittal can't be used against the civil plaintiff: Generally speaking, every litigant is entitled to have a chance to prove his case in court once, and this plaintiff didn't have that chance at the criminal trial (since the parties at the criminal trial were the government and the defendant, not the victim and the defendant). If the defendant had lost at the criminal trial (see #2 above), he would have had his chance to prove that he wasn't guilty by a reasonable doubt (or, to be precise, his chance to have a jury reject the prosecution's attempts to prove its case), which is why that conviction could be used against the defendant in a future civil case. But a defendant's acquittal can't be used against a plaintiff in a future case, because the plaintiff wasn't involved in the earlier trial.
4. Now let's change the order: Say you're found liable in a civil trial, and are then prosecuted criminally. Can the prosecution use the verdict against you as proof that you're guilty (at least to the factual elements that are shared between the definition of the tort and of the crime)? No, for two reasons. First, the civil verdict merely reflects that the factfinder thought your liability was shown by a preponderance of the evidence or, in most punitive damages cases, by clear and convincing evidence; that's not enough in a criminal case, where a factfinder must find you liable beyond a reasonable doubt.
Second, the Jury Trial Clause is generally understood as securing to all criminal defendants (at least in cases where the crime was punishable by more than six months' imprisoment) a right to have a criminal jury find their guilt. This means that the prosecution must prove the facts to the satisfaction of that criminal jury, and not of an earlier judge or civil jury.
5. And to complete the list, say you're found not liable in a civil trial, and are then prosecuted criminally. The earlier civil jury concluded that you're not liable even by a preponderance of the evidence, which is to say that you're no more than 50% likely to be guilty. Shouldn't that prevent a criminal jury from finding you guilty beyond a reasonable doubt?
No, for the second reason given in item 3 above: The government as prosecutor isn't bound by the earlier verdict because it wasn't a party in the case. Maybe the plaintiff did a lousy job of presenting the case. Maybe the plaintiff even deliberately took it easy on defendant (not much of an incentive for that now, but there might be if a civil verdict of nonliability could preclude a future criminal prosecution). The government as prosecutor is entitled to its own chance at proving the defendant guilty, even if the earlier civil plaintiff had failed.