See also Impeachment of verdict. Federal Rule of Evidence 606(b) is grounded in the common-law rule against admission of jury testimony to impeach a verdict and the exception for juror testimony relating to extraneous influences. See Government of the Virgin Islands v. Gereau, 523 F.2d 140, 149, n. 22 (CA3 1975); S. Rep. No. 93-1277, p. 13 (1974) (observing that Rule 606(b) 'embodied long-accepted Federal law').
Rule 606(b) states: 'Upon an inquiry into the validity of a verdict or indictment, a juror may not testify as to any matter or statement occurring during the course of the jury's deliberations or to the effect of anything upon his or any other juror's mind or emotions as influencing him to assent to or dissent from the verdict or indictment or concerning his mental processes in connection therewith, except that a juror may testify on the question whether extraneous prejudicial information was improperly brought to the jury's attention or whether any outside influence was improperly brought to bear upon any juror. Nor may his affidavit or evidence of any statement by him concerning a matter about which he would be precluded from testifying be received for these purposes.'
See ...