Gardner v. Malone, presents this problem: In what circumstances and by what evidence may a jury verdict be impeached for alleged misconduct in the jury-room? As an original proposition it would seem that, consonant with our notions of a fair trial, an improperly reached verdict should be subject to timely impeachment in every case. And further, there is no more logical means of proving such misconduct than by the testimony or affidavits of the jurors themselves. This, however, is not the law. Most American jurisdictions will not admit the testimony or affidavits of jurors to impeach their verdicts under any circumstances. This rule has two bases. The first is Vaise v. Delaval, written by Lord Mansfield in 1785. Premised on the idea that testimony of a juror regarding his own misconduct is inadmissible, while that of an eavesdropper to the same act may be heard, Vaise is obviously an historic anomaly.
Richard E. Keefe,
Washington Case Law,
Practice and Procedure—Impeachment of Verdicts by Jurors' Affidavits,
Wash. L. & Rev.
Available at: https://digitalcommons.law.uw.edu/wlr/vol38/iss2/12