Prosecutorial misconduct

The prosecutor's duty in a criminal prosecution is to seek justice.l866 Although the prosecutor should "prosecute with earnestness and vigor," she may not use "improper methods calculated to produce a wrongful conviction." 1867 Generally, the use of such methods is grounds for mistrial or reversal of a conviction if it results in an unfair trial violating the Due Process Clause. If the prosecutorial misconduct is intended to cause a mistrial, the Double Jeopardy Clause may bar further prosecution. 1868

Improper Comments. To justify reversal of a conviction, it is not enough that the prosecutor's remarks or conduct were improper: "It]he relevant question is whether the prosecutor's comments `so infected the trial with unfairness as to make the resulting conviction a denial of due process.' "Is 1869 Generally, a court will not reverse a conviction because of improper comments by the prosecutor if evidence of the defendant's guilt is overwhelming,l870 if the trial court offers curative instructions to the jury,1871 if the misconduct has little cumulative effect on the jury,l872 or if a combination of these three factors ensures no violation of due process.l873

A prosecutor should avoid making unfair or improper remarks about the defendant,l874 defense counsel,l875 or a defense witness.'876 She may not express personal opinions about the defendant's guilt or credibility18'' or about matters requiring expert knowledge.'878 Furthermore, the prosecutor may not comment on the defendant's failure to testify at trial.'9 Also, with certain exceptions, she may not refer to previous convictions, current guilty pleas, or other bad acts of the defendant, codefendants, or co-conspirators.l880 The prosecutor may not vouch for the credibility of government witnesses"""1 or allude to her own oath of office to bolster the government's case.l882 The prosecutor also may not appeal to jurors to act as a conscience for the community or make other remarks likely to inflame the passions of the jurors, if intended to lead them to convict for an improper reason.l883 Otherwise improper comments may be excused under the "invited reply" doctrine, if the prosecutor's remarks were an appropriate response to statements or arguments made by the defense.1884

Other Types of Misconduct. Although the line between acceptable and improper advocacy is not always clear, courts have consistently found certain types of prosecutorial conduct improper. The prosecutor may not knowingly present false testimony1885 and has a duty to correct testimony that she knows is false.1886 Furthermore, the prosecutor may not attempt to introduce inadmissible evidence' and must disclose evidence favorable to the defendant if the defendant requests it.lass

Prosecutors may not make material misstatements of law1889 or fact.89 The prosecutor should confine her opening statement to evidence she intends to offer that she believes will be admissible, and limit her closing argument to evidence on the record and permissible inferences therefrom.l891 Repeated misstatements that go uncorrected may be grounds for ordering a new trial or reversal on appeal.1892

In Doyle v. Ohio,1893 the Supreme Court held that a prosecutor may not use a defendant's postarrest, post-Miranda silence for impeachment purposes because the Miranda warnings implicitly assure a defendant that she will not be penalized for remaining silent.l894 Nonetheless, impeachment with prearrest silence,l895 or postarrest, pre-Miranda silencel896 is proper because the defendant could not have relied on Miranda's implicit assurance.

It is improper for a prosecutor to call a third-party witness knowing that the witness will invoke her Fifth Amendment privilege against self-incrimination, because the jury might improperly infer guilt from the witness's silence.1897 In addition, the prosecutor may not suggest that the defendant's retention of counsel indicates guilt.1898

Appellate Review. Appellate courts will usually defer to the trial judge's conclusions about the effects of prosecutorial misconduct during trial.1199 Prosecutorial misconduct, including Doyle violations,'90 is subject to harmless error review and will constitute harmless error if the appellate court determines with "fair assurance . . . that the judgment was not substantially swayed by the error."1901 To preserve a claim of improper conduct by the prosecutor on appeal, the defendant must make a timely objection.l9 Otherwise, an appellate court will only reverse the conviction if the lower court's decision to allow the prosecutor's conduct constituted "plain error." 1903

In Brecht v. Abrahamson,'4 the Supreme Court held that habeas corpus relief for trial errors involving prosecutorial misconduct should only be granted if the error "had substantial and injurious effect or influence in determining the jury's verdict." 1905

1866. Berger v. U.S., 295 U.S. 78, 88 (1935).

1867. Id. Misconduct by the prosecutor during the sentencing phase of capital trial is discussed in Improper Influences in Capital Cases in CAPITAL PUNISHMENT in Part IV. 1868. The ability to retry a defendant after the declaration of a mistrial due to prosecutorial misconduct is discussed in Retrial Following Mistrial in DOUBLE JEOPARDY in Part II. 1869. Darden v. Wainwright, 477 U.S. 168, 181 (1986) (quoting Donnelly v. DeChristoforo, 416 U.S. 637, 643 (1974)); U.S. v. Young, 470 U.S. 1, 11-12 (1985) (criminal conviction not readily overturned on basis of prosecutor's comments alone; statements must be viewed in context of entire proceeding to determine whether conduct affected fairness of trial); U.S. v. Hasting, 461 U.S. 499, 505-07 (1983) (deterrence of prosecutorial misconduct inappropriate basis for reversal of conviction when prosecutor's remark regarding defendant's failure to challenge charges not flagrant violation of defendant's rights and less drastic means to deter objectionable conduct available).