I know that often a potential juror who is a lawyer, or anyone with direct expertise relevant to a case, will be removed by one side or the other. However, this doesn't always happen, if for example all the peremptory challenges were used up on other more worrying individuals.

So let's say juror Bob is someone whose profession is directly related to a major topic in a trial. Both the defendant and the prosecutor had expert witnesses making opposite claims about the evidence, and both claims were complicated enough that the average juror is going to have difficulty judging which one is correct. Still, all the other evidence would seem to suggest the defendant was innocent and the jury seems ready to say that when in steps Bob. Bob declares the expert witness for the defendant was clearly wrong because of some reason X, and given that fact they should trust he prosecution's witness that the evidence was damning.

The jury figures Bob should qualify as an expert witness, one that's theoretically unbiased and safe to use as a tie breaker. Thus given Bob's insistence that the defendants argument was fallacious the others are convinced to find him guilty.

Only once Bob heads home he does some quick research and realizes he had misremembered subject X and his argument was therefor wrong. The defendant's expert witness's argument was sound and Bob now believes not only was he wrong but that the defendant was innocent; yet largely due to Bob the man was found guilty. Bob wants to make amends and contacts the lawyer for the defendant to explain what happened.

Does the defendant have any recourse in this case? Or did one person's bad memory doom an innocent man?

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    I know that often a potential juror who is a lawyer ... will be removed by one side or the other Lawyers aren't automatically disqualified? Really? Commented Jan 7, 2023 at 16:06
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    @JohnGordon law.stackexchange.com/a/4560/27339
    – Anyon
    Commented Jan 7, 2023 at 16:33
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    Jurors are allowed to be experts in the thing that's being tried.
    – Richard
    Commented Jan 7, 2023 at 17:32
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    It's not "bad memory" that would've doomed someone, but rather poor judgement in whether and how to share that information. If Bob is actually an expert, there's a vanishingly small possibility that they'd confidently be wrong when cautiously exercising reasonable judgement in that situation. If Bob just read something on the internet one time, they should probably just keep their mouth shut and assume the lawyers involved would've found and presented that information if there were sufficient merit to it. Other jurors also shouldn't just "figure Bob should qualify as an expert witness".
    – NotThatGuy
    Commented Jan 9, 2023 at 12:36

4 Answers 4


It is an almost-universal rule that a juror cannot testify to impeach a jury verdict. FRE 606 says

A juror may not testify as a witness before the other jurors at the trial...

During an inquiry into the validity of a verdict or indictment, a juror may not testify about any statement made or incident that occurred during the jury’s deliberations; the effect of anything on that juror’s or another juror’s vote; or any juror’s mental processes concerning the verdict or indictment. The court may not receive a juror’s affidavit or evidence of a juror’s statement on these matters.

There are exceptions, however.

A juror may testify about whether:

(A) extraneous prejudicial information was improperly brought to the jury’s attention;

(B) an outside influence was improperly brought to bear on any juror; or

(C) a mistake was made in entering the verdict on the verdict form.

"Outside influence" refers to "things outside the jury room". In Tanner v. US, the court interpreted the rule as saying that even if half the jurors were high during deliberation, jurors cannot testify about this to impeach the verdict (likewise held in Warger v. Shauers). However, Peña-Rodrigues v. Colorado admits another exception, that

[w]here a juror makes a clear statement indicating that he or she relied on racial stereotypes or animus to convict a criminal defend ant, the Sixth Amendment requires that the no-impeachment rule give way in order to permit the trial court to consider the evidence of the juror’s statement and any resulting denial of the jury trial guarantee

The situation that you describe is thus outside the exceptions to the no-impeachment rule.

There can be a post-verdict escape, if the jurisdiction has a law like RCW 10.61.060:

When there is a verdict of conviction in which it appears to the court that the jury have mistaken the law, the court may explain the reason for that opinion, and direct the jury to reconsider the verdict; and if after such reconsideration they return the same verdict it must be entered, but it shall be good cause for new trial. When there is a verdict of acquittal the court cannot require the jury to reconsider it.

But this only related to jury mistakes of law, not mistakes of fact. In the situation that you describe, Bib cannot erase his prior misconduct by doing something to nullify the jury's vote (under his influence).

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    Does "(A) extraneous prejudicial information was improperly brought to the jury’s attention;" not apply in the OP's example? The information provided by the juror is extraneous in the sense that it was not presented in court, it is prejudicial in the sense that it swayed jury members to vote differently, and it was improperly brought in the sense that it is not proper for a juror to act as if they are an expert witness in the case.
    – kaya3
    Commented Jan 7, 2023 at 15:36
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    In relation to @kaya3's point, at what point does a juror's prior knowledge count as "extraneous information"? Suppose that in a robbery trial, the defendant testifies, "I stabbed the person behind the counter with a knife." Presumably, the state doesn't need to bring in expert witnesses to testify that a knife is a deadly weapon and stabbing is generally an act of violence; the jurors can rely on their prior knowledge of those facts. Commented Jan 8, 2023 at 0:43

What should have happened

Jurors will be instructed along the following lines (Model Jury Instructions, 8.4 - Outside Information):

The only information that you may consider is the evidence that has been put before you in the courtroom. You must disregard completely any information from radio, television, or newspaper accounts, Internet sources, Twitter, Facebook, or any other social media, that you have heard, seen or read about in respect of this case, or about any of the persons or places involved or mentioned in it. Any other information about the case from outside the courtroom, is not evidence.

They will also be instructed about reasonable doubt in relation to expert evidence:

The issue on which these experts... differ is an essential element that the Crown must prove beyond a reasonable doubt. Before you accept the opinion of the Crown’s expert on this issue you must be satisfied beyond a reasonable doubt that s/he is correct. If you are not sure that s/he is correct, then the Crown has failed to prove beyond a reasonable doubt that essential element of the offence charged.

Given that the jurors were waffling, they would have had reasonable doubt and should have acquitted.

Regardless, once a jury verdict is rendered, it is not possible for the trial judge to alter the verdict except where the judge learns that the jury did not render the verdict it intended (R. v. Burke, 2002 SCC 55). Even a judge learning of potential juror bias does not have the power to declare a mistrial after the verdict is rendered: R. v. Halcrow, 2008 ABCA 319.

There are very narrow grounds to appeal a verdict based on a problem with what the jury did

There may be very limited opportunities on appeal:

  • if one can show a reasonable apprehension of bias based on evidence that does not include matters intrinsic to the jury room (e.g. R. v. Mehl, 2021 BCCA 264)
  • if the verdict was unreasonable in the sense that it was a verdict that no jury, properly instructed and acting judicially, could reasonably return—this is the standard referred to in ohwilleke's answer (in the circumstances you've described, it seemed that there was evidence in the record that the jury could have been convinced by, so your scenario does not seem to meet this high standard for an unreasonable verdict)

Jury-secrecy rules prohibit matters internal to the jury from ever being introduced as evidence

Above all of this are the statutory and common-law jury secrecy rules. The rule in Canada is this (from R. v. Pan; R. v. Sawyer, 2001 SCC 42):

statements made, opinions expressed, arguments advanced and votes cast by members of a jury in the course of their deliberations are inadmissible in any legal proceedings. In particular, jurors may not testify about the effect of anything on their or other jurors’ minds, emotions or ultimate decision. On the other hand, the common law rule does not render inadmissible evidence of facts, statements or events extrinsic to the deliberation process, whether originating from a juror or from a third party, that may have tainted the verdict.

The dividing line between intrinsic matters protected by the jury secrecy rules and extrinsic matters that might be able to be revealed is not always clear, but the evidence you've described seems to be an intrinsic matter:

[61] Jurors are expected to bring to their task their entire life’s experiences. It is on the basis of what they know about human behaviour, knowledge that they have obviously acquired outside the courtroom, that they are requested to assess credibility and to draw inferences from proven facts. Even though not the object of evidence tendered in the trial, an opinion, a piece of general information, or even some specialized knowledge that a juror may reveal in the course of the deliberations, is not an extrinsic matter. Typically, such information would not be the object of evidence tendered at trial. It would be viewed as either irrelevant, too remote, or as attempting to usurp the functions of the jury. On the other hand, if a juror, or a third party, conveys to the jury information that bears directly on the case at hand that was not admitted at trial, by reason of an oversight or a strategic decision by counsel or, worse yet, by operation of an exclusionary rule of admissibility, then it is truly a matter “extrinsic” to the deliberation process and the fact that it was introduced into that process may be revealed.

[62] The line between matters of general knowledge and information that bears directly on the case may not always be evident. For example, if a juror shares with his fellow jurors his detailed familiarity with the location where the crime was alleged to have been committed, this may be viewed as an intrinsic matter protected by the secrecy rule. If the same juror, however, went on a visit to the site, took photographs and brought them back to the jury room to support his interpretation of the facts at issue, this may be extrinsic, outside information that falls outside the secrecy rule.


The verdict stands

An appeal may be made to overturn a conviction and declare a mistrial where there is evidence of juror misconduct. Where this emerges before the verdict, the juror may be discharged and, if the misconduct has contaminated the rest of the jury, a mistrial may be declared. In NSW juror misconduct is a crime but this is not the case in all Australian jurisdictions.

There is no juror misconduct here

Juror misconduct only involves considering or seeking information or material that has not been entered into evidence in the trial.

Bob exercised his judgement, including his general skill and knowledge in the field, in deciding which expert evidence he preferred - this is not only permitted, it is required. He shared his reasoning with the rest of the jury - totally fine. They deferred to his judgement - also fine, juries decide how they will decide what they have to decide.

At no point did Bob or any other jury member seek or rely on any information that was not in evidence while they were deliberating.

If Bob had done “some quick research” during the trial, that would be jury misconduct

Bob is just an ex-juror who now regrets the verdict they gave - the world is full of them.

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    This seems like a philosophical question, but perhaps there is an objective answer in law - how do we determine whether Bob's prior knowledge is "information"? It sounds to me from the question like Bob didn't just tell the other jurors what his judgement is, he also made an argument based on his own knowledge which convinced the other jurors. Couldn't telling that knowledge to the other jurors count as "informing" them?
    – kaya3
    Commented Jan 7, 2023 at 15:43
  • "If Bob had done “some quick research” during the trial, that would be jury misconduct" What if this research merely involves Bob, say, poring through similar court cases and their ultimate outcomes?
    – moonman239
    Commented Jan 9, 2023 at 21:47
  • @moonman239 hell, yes. Any material that isn’t in evidence is extrinsic. Court judgements are specifically problematic because they will contain interpretations of the law which, in a jury trial, is the exclusive preserve of the judge. The judge tells the jury what the law is; a juror that tries to decide the law is engaging in misconduct.
    – Dale M
    Commented Jan 9, 2023 at 21:50
  • In a similar vein, what if Bob were to hear the expert and then take, say, a college course, to better understand the expert's field of expertise, with little or no risk of hearing facts about the case at hand? For example, if an expert testifies that blood splatter indicates what happened at the time of a murder, Bob may wish to research the biology and physics of blood splatter. Is this impermissible as well?
    – moonman239
    Commented Jan 9, 2023 at 21:55
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    @moonman239 was the curriculum of that college course entered into evidence? No? Juror misconduct. The expert is the expert - acknowledged by the court and the law as such. Bob is just a juror - he is entitled to believe or disbelieve the expert, he’s not allowed to second-guess them.
    – Dale M
    Commented Jan 9, 2023 at 21:57

Rather than inquiring into what the jury actually did (except in very narrow exceptions identified by user6725), courts in common law countries reviewing convictions on appeal review the evidence that was presented at trial.

The appellate courts then uphold the jury verdict in every case in which a hypothetical reasonable jury could conclude that a conviction was appropriate based upon the evidence presented at trial, whether or not the jury's verdict was actually reached for the reason or not.

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