How can criminal law precedent ever be changed in the prosecutions favor?

Disclaimer: I’m not a lawyer which is why I’m asking this question, so it is entirely possible I am totally misunderstanding the situation.

So as I understand it legal precedent gets changed by having a court case based on that precedent goes through appeals all the way up to the supreme court which then rules that the precedent has changed, or at the very least that the lower courts understanding of the precedent was incorrect. But due to the rules against double jeopardy, if a defendant is found guilty, the state can’t retry him or appeal that decision.

So suppose at some point a judge in a court case established, for example, that police looking at facebook posts is an illegal search and so such evidence should be thrown out. Is there anyway to have this issue revisited? All cases in which the verdict would hinge on such evidence would begin with the lower court following precedent and throwing out the evidence resulting in an acquittal and so not be open to appeal.

If I have this right, then it appears that our legal system by design is on a ratchet which will continually expand rights in favor of the accused.

IANAL, but the prosecutor doesn’t appeal a verdict, per se. S/he appeals a misapplication of a law. I believe they have to file the appeal before the verdict is reached. In the example you cite, the prosecutor could appeal that the ruling. This appeal could go all the way to the Supreme court

IANAL, but one thing that can happen is that the Supreme Court can hand down a decision that seems to establish a broad and clear standard about something (going through a defendant’s Facebook posts is unconstitutional). And maybe that defendant walks*. But then, in other cases, police do things that are not quite the exact same thing as what the police did in the first case. Citing that first precedent, those new defendants appeal to the Supreme Court–but perhaps SCOTUS has some new members by now, and at any rate, they don’t want to set up “a ratchet which will continually expand rights in favor of the accused” (these are federal judges we’re talking about here, and at least some of them are probably fairly “law and order” types). So, in these new cases, even if they don’t overturn the original ruling, they whittle away at it to the point where it turns out it means a lot less than people might have originally thought. (“Searching a defendant’s Tweets is a completely different thing than searching his Facebook posts. Guilty verdict sustained!” “Well, they didn’t actually search his Facebook posts, they looked at the Facebook posts of his friends and family–which technically were all ‘consensual searches’–and were able to reconstruct what he’d posted by seeing where other people had re-posted his original posts. Guilty verdict sustained!”** And so on.

And, if the original verdict is weakened enough, some police department or state legislature may eventually say to hell with it, and straight-up search some guys Facebook posts/pass a law allowing such searches, with the idea that (based on those more-recent precedents) the current Supreme Court will probably overturn that Commie criminal-coddling decision entirely. I don’t know of any “criminal defendant”-type decisions where that’s happened, but in Roe v. Wade we’ve seen both the “whittle away at the decision” process, and now some state legislatures are simply passing laws that directly contravene Roe, because they’re hoping the current SCOTUS will overturn Roe entirely.
*Although not necessarily. Even if the results of the illegal search or unlawful interrogation or whatever are thrown out, I believe the remedy frequently is simply to order a new trial, at which point the defendant may be found guilty anyway by a new jury based on other evidence that wasn’t thrown out.
**Full disclosure, I don’t actually really use Facebook that much, and am sort of vague on the details of how it works.

But often the ruling in cases of conviction can also have the effect of changing precedent to the detriment of defendants. A judge could easily rule that the hypothetical facebook rule does not apply in the circumstances… i.e. when a third party brings the facebook data to the police, if the post is liked by someone who did give permission, etc. This goes up the appeal chain - how blanket is the provision? The court then could revisit the ban or (more likely) change the limitations. We’ve seen the ban on questioning the defendant without council fine-tuned to this level with numerous court cases… I think if the defendant does not explicitly say “I want a lawyer” so intent is clear, if the defendant says things unsolicited, if the defendant says things to a jailhouse informant, etc.

I take it from your hypothetical you’re thinking mainly of Constitutional protections, but sometimes criminal law jurisprudence is just based on statutes, which are a lot easier to change. So maybe the decision wasn’t that looking at the defendant’s Facebook posts was a Fourth Amendment violation, but rather that it violated SB100, which the new crop of legislators don’t care for.

But even Constitutional protections can change over time. I’ve always been fascinated by the concept of “reasonable expectation of privacy,” because it seems that routine violations by the police could, in theory, actually change a reasonable person’s expectations, and therefore expand the police’s authority. A lot of recent decisions have had to do with the use of technology, and we’re learning more every day about how major corporations can and do track us without our knowledge or express consent. I think at this point it’s clear to anyone with common sense that there’s no reasonable expectation of privacy in anything you post publicly on the internet, but what about when you limit the audience? What if you set the privacy to “only me”?

I take it you mean whether interpretation of law can be made more prosecution friendly.
The answer to that is that there is a rule of interpretation called the “rule of lenity”, that multiple interpretations are possible, the one most favourable to the defendant will be adopted.


The term is interlocutory appeal, an appeal of a trial court’s ruling prior to judgement.

So suppose in the hypothetical that a trial court judge make a ruling to exclude evidence gathered from a Facebook profile without a warrant. At that point the prosecutor could request a recess in order to file an interlocutory appeal requesting the relevant appeals court overturn the trial court’s ruling excluding the evidence. And if the appeals court overturns the trial court’s ruling then they issue a decision which sends the matter back to the trial court with an order to admit the evidence at issue. The defendant could appeal the appeal’s court’s ruling to the relevant state or US high court.

Generally the state high court* and the US Supreme Court are not required to hear an appeal and could let the appeals court or trial court’s ruling stand without hearing arguments.

And if the appeals court initially upholds the trial court’s exclusion of evidence the prosecutor could attempt to appeal that ruling to the relevant state high court or US Supreme Court.

  • The name of the highest court of appeal in a state court system is not uniformly called that state’s “Supreme Court”. In New York state The Supreme Court of the State of New York is a trial court, where most trials in cases of general jurisdictions would be held.

Obviously not a universal answer to the OP, but Brennan v HMA was a Scottish appeal that set/confirmed the precedent that intoxication could not ever be used as defence in a murder trial in Scotland.

It seems that the defence tried to prove insanity (a “special defence” in Scotland) and alternatively requested that the jury find the accused guilty of the lesser crime of culpable homicide. The original judge forbade the jury from each of these verdicts - I believe he did this in order to intentionally force an appeal and thereby get the higher court to forever banish these defences.