Does partiality discredit witnesses?
<p>In criminal trials, when a regular (non-expert) witness does not like the defendant (and admits it when asked), does that alone give a valid reason to discredit them to any extent at all?</p>
<p>Can the jury be given directions along the lines &quot;<em>this witness does not like the defendant, and that may have been why they testify against him, and hence they may lie</em>&quot;?</p>
<p>On the one hand, it makes perfect sense.</p>
<p>But on the other, if such witnesses were routinely legally discredited, then no victim's testimony would ever be allowed weight.</p>
<p>Where does the balance lie? Are there any rules, principles, tests that are applied to decide whether witnesses disliking defendants are to be believed or not, or to what extent?</p>
<p>Related, but not dupe as it is much broader: <a href="https://law.stackexchange.com/questions/67756/witness-credibility-questions-on-cross-examination">Witness credibility questions on cross-examination</a></p>

<h2>Only a jury can answer your question, and then on a case-by-case basis.</h2>
<p>When a witness testifies, the question of whether and to what extent to believe/disbelieve a witness is nearly 100% the decision of the jury (or the judge in a bench trial).</p>
<p>In a criminal trial, at least, if a thousand disinterested nuns can take the stand and give identical testimony that Defendant robbed the bank, and Defendant's mother says he was actually with her on a Bahamas cruise at the time of the robbery (nevermind the fact that he was arrested exiting the bank), the jury is 100 percent free to conclude the nuns are lying and the mother is telling the truth.</p>
<p>Likewise, if Superman is on trial, the jury would be free to believe or disbelieve whomever they chose if the only evidence they had to rely on was (1) Lex Luthor's testimony that he hates Superman and saw him kill Doctor Light; and (2) Lois Lane's testimony that she loves Superman and saw Lex Luthor do it.</p>
<h3>The jury's right to weigh credibility is hundreds of years old.</h3>
<p>The question of how to weigh this evidence -- and the answer, which is that it is essentially left entirely to the jury -- is among the most well-settled principles of common-law evidence. <em>See</em>, <em>e.g.</em>, Blackstone, <em>Commentaries</em>, 3:354 (1768) (&quot;All others are competent witnesses; though the jury from other circumstances will judge of their credibility.&quot;).</p>
<p>Jury instructions therefore routinely advise jurors that they may consider a witness's prejudices for or against the defendant and conclude that his statements are not reliable, whether because he is lying or simply too biased to reliably remember the events in question. <a href="https://casetext.com/case/united-states-v-abel" rel="nofollow noreferrer"><em>United States v. Abel</em>, 469 U.S. 45, 52, 105 S. Ct. 465, 469 (1984)</a> (&quot;Bias is a term used in the 'common law of evidence' to describe the relationship between a party and a witness which might lead the witness to slant, unconsciously or otherwise, his testimony in favor of or against a party. Bias may be induced by a witness' like, dislike, or fear of a party, or by the witness' self-interest.&quot;).</p>
<p>You can follow the trail of cases supporting this position quite a ways back. I stopped when I reached <a href="https://casetext.com/case/honegger-et-al-v-wettstein-et-al" rel="nofollow noreferrer"><em>Honegger v. Wettstein</em>, 94 N.Y. 252 (1883)</a>, a case where a manufacturer sued members of a firm that had bought its goods but never paid. At trial, a principal of the firm testified about the invoiced amount to be paid, and because the testimony was uncontradicted, the judge ordered a directed verdict in favor of the buyers. But the New York Court of Appeals reversed, holding that the credibility of a biased witness's testimony must be left to the jury:</p>
<blockquote>
<p>Although not contradicted, he was an interested party, and had a direct interest in increasing the fund in the hands of the receiver, and in preventing its payment to the plaintiffs. His evidence was given for the purpose of showing the alleged violation of law by the plaintiffs, and in explanation of the three invoices which were made of the goods, of which duplicates were made, and it was a fair question for the jury to say whether he might not have been influenced by the circumstances stated.</p>
</blockquote>
<p>Ten years later, the Supreme Court addressed your question a bit more directly. In <a href="https://casetext.com/case/reagan-v-united-states" rel="nofollow noreferrer"><em>Reagan v. United States</em>, 157 U.S. 301 (1895)</a>, a defendant who took the stand was convicted after the trial court told the jury that &quot;Where the witness has a direct personal interest in the result of the suit the temptation is strong to color, pervert, or withhold the facts.&quot; But the Supreme Court affirmed the conviction, holding that &quot;the court may, and sometimes ought, to remind the jury that interest creates a motive for false testimony.&quot;</p>
<h3>Modern courts permit, but do not require, instructions highlighting a specific witness's bias.</h3>
<p>These cases of course deal with witnesses who have a bias <em>in favor</em> of a party, but the rule is no different in cases where a witness, as in your question, admits to a bias <em>against</em> a party. In <a href="https://casetext.com/case/us-v-coleman-197" rel="nofollow noreferrer"><em>United States v. Coleman</em>, 887 F.2d 266 (6th Cir. 1989)</a>, for instance, a defendant was charged with conspiracy to commit arson. Because the only direct evidence of his agreement to the arson was testimony from a witness &quot;who admitted a bias against defendant,&quot; he sought a judgment of acquittal, but the trial court denied his motion and sent the case to a jury. The Sixth Circuit affirmed his conviction, holding that it was up to the jury to decide whether the witness was credible:</p>
<blockquote>
<p>As defendant points out on appeal, Boscaglia's credibility was very much in issue at trial, but the jury resolved the issue against defendant. The jury's decision on &quot;the credibility of witnesses is not reviewable on appeal.&quot;</p>
</blockquote>
<p>Although such instructions are <em>allowed</em>, this does not mean that a court is always <em>required</em> to give an instruction addressing the credibility of a specific witness. Depending on who the witness is biased for/against, there are likewise cases saying that no instruction was necessarily required, <a href="https://casetext.com/case/kovacich-v-spearman" rel="nofollow noreferrer"><em>Kovacich v. Spearman</em>, No. 2:13-cv-0985 KJM DAD P, 2015 U.S. Dist. LEXIS 108233 (E.D. Cal. Aug. 14, 2015)</a> (denying habeas claim by defendant who unsuccessfully sought jury instructions highlighting the bias of the investigating officer), or that such an instruction is a bad idea but not disallowed, <a href="https://casetext.com/case/us-v-jones-1156" rel="nofollow noreferrer"><em>United States v. Jones</em>, 372 F. App'x 343, 345 (3d Cir. 2010)</a> (&quot;While such an instruction that singles out the defendant's interest in the case is not advisable, we find that here it did not constitute reversible error.&quot;).</p>
<p>I haven't found any saying that such an instruction was a reversible error, though I suspect that there are cases out there in which verdicts were reversed because the judge went overboard in suggesting to a jury how much credibility they should extend an admittedly biased witness.</p>

<h2>Partiality <em>may</em> discredit a witness</h2>
<p>But that, and the extent to which it discounts their evidence is a matter for the jury.</p>
<p>From the <a href="/questions/tagged/new-south-wales" class="post-tag" title="show questions tagged &#39;new-south-wales&#39;" rel="tag">new-south-wales</a> <a href="https://www.judcom.nsw.gov.au/publications/benchbks/criminal/onus_and_standard_of_proof.html#p3-625" rel="nofollow noreferrer">Criminal Trials Bench Book</a>:</p>
<blockquote>
<p><strong>[3-625] Motive to lie and the onus of proof</strong></p>
<p><strong>Crown witnesses</strong></p>
<ol>
<li><p>A motive to lie or to be untruthful, if it is established, may “substantially affect the assessment of the credibility of the witness”: ss 103, 106(2)(a) Evidence Act 1995. <strong>Where there is evidence that a Crown witness has a motive to lie, the jury’s task is to consider that evidence and to determine whether they are nevertheless satisfied that the evidence given is true</strong>: <em>South v R</em> [2007] NSWCCA 117 at [42]; MAJW v R [2009] NSWCCA 255 at [31]. The jury’s task does not include speculating whether there is some other reason why the Crown witness would lie: <em>Brown v R</em> [2008] NSWCCA 306 at [50]. Nor does it include acceptance of the Crown witness’s evidence unless some positive answer to that question is given by the accused: <em>South v R</em> at [42].</p>
</li>
<li><p>If the defence case directly asserts a motive to lie on the part of a central Crown witness, the summing-up should contain clear directions on the onus of proof, including a direction that the accused bears no onus to prove a motive to lie and that rejection of the motive asserted does not necessarily justify a conclusion that the evidence of the witness is truthful: <em>Doe v R</em> [2008] NSWCCA 203 at [58]. Where the defence does not directly raise the issue, it is impermissible for the prosecutor to submit (for the purpose of promoting the acceptance of a Crown witness as a witness of truth) that the accused did not advance a motive to lie. The jury should not be given the impression that the accused bears some onus of proving the existence of a motive for the fabrication of the allegations against him or her: <em>Doe v R</em> at [59]–[60].</p>
</li>
</ol>
<p><strong>The accused</strong></p>
<ol start="3">
<li><p>It is impermissible to cross-examine an accused to show that he or she does not know of any reason why the complainant (or indeed a central Crown witness) has a motive to lie: <em>Palmer v The Queen</em> (1998) 193 CLR 1 at [8]; <em>Doe v R</em> at [59]. The question focuses the jury’s attention on irrelevant material and invites them to accept the evidence unless some positive answer is given by the accused: <em>Palmer v The Queen</em> at [8]. An open-ended question to the accused, “why would the complainant lie?”, “simply should never be asked” by a prosecutor in a trial: <em>Doe v R</em> at [54]; <em>South v R</em> [2007] NSWCCA 117 at [44]; <em>Causevic v R</em> [2008] NSWCCA 238 at [38]. If in closing addresses the prosecutor makes a comment or asks a rhetorical question to that effect when the issue has not been raised, the judge should give full, firm and clear directions on the onus of proof, including a direction that the accused bears no onus to prove a motive to lie: <em>Palmer v The Queen</em> at [7]–[8]; <em>Doe v R</em> at [59]–[60]; <em>Cusack v R</em> [2009] NSWCCA 155 at [105].</p>
</li>
<li><p>The evidence of an accused person is subject to the tests which are generally applicable to witnesses in a criminal trial: <em>Robinson v The Queen</em> (1991) 180 CLR 531 at 536. However, the trial judge should refrain from directing the jury that the accused’s interest in the outcome of the proceedings is a factor relevant to assessing his or her credibility as a witness: <em>Robinson v The Queen</em> at 535–536; MAJW v R [2009] NSWCCA 255 at [37]–[38]. <em>Robinson v The Queen</em> did not create a new rule. It applied a more general principle that directions should not deflect the jury from its fundamental task of deciding whether the prosecution had proved its case beyond reasonable doubt: <em>Hargraves v The Queen</em> (2011) 245 CLR 257 at [46]. Nevertheless trial judges must not instruct juries in terms of the accused’s interest in the outcome of the proceedings whether as a direction of law or as a judicial comment on the facts: <em>Hargraves v The Queen</em> at [46]. A direction of that kind seriously impairs the fairness of the trial and undermines the presumption of innocence: <em>Robinson v The Queen</em> at 535.</p>
</li>
</ol>
<p>See further Cross-examination of defendant as to credibility at [1-343] and Consciousness of Guilt, Lies and Flight at [2-950]ff.</p>
</blockquote>

<blockquote>
<p>when a regular (non-expert) witness does not like the defendant (and admits it when asked), does that alone give a valid reason to discredit them to any extent at all?</p>
</blockquote>
<p>Not alone. It is simply another factor the jury may consider in weighing a witness's credibility. <a href="https://www.leagle.com/decision/infco20130909092" rel="nofollow noreferrer"><em>U.S. v. Bonilla-Guizar</em>, 729 F.3d 1179, 1186 (2013)</a>.</p>
<p>If anything, from a practical standpoint, the witness's disclosure of bias suggests that his testimony might be more reliable insofar as the witness is prioritizing truthful answers (even those that at the outset might prejudice the testimony altogether) rather than credibility calculations. A transparent disclosure of [dis-]liking the defendant gives the jury a straight-forward element on how much credibility the testimony deserves. The court in <em>Bonilla-Guizar</em> points out that the witness's admission of bias &quot;<em>may have had the effect of enhancing his credibility</em>&quot;.</p>
<p><a href="https://www.leagle.com/decision/ininco20100308180" rel="nofollow noreferrer"><em>Embry v. State</em>, 923 N.E.2d 1 (2010)</a> addresses evidentiary issues of which the premise is the witness's exposed bias against the defendant. For instance, the opinion points out that &quot;<em>[in] some jurisdictions [...] the State may respond by introducing the defendant's prior uncharged misconduct to explain the witness's antipathy</em>&quot;, <em>Id at 7-8</em>. The <em>Embry</em> court took the opposite approach only as to the <em>prior uncharged misconduct</em>, which is short singlehandedly dismissing the witness's testimony.</p>
<p>See also <a href="https://www.leagle.com/decision/1990984794sw2d1901983" rel="nofollow noreferrer"><em>State v. Wacaser</em>, 794 S.W.2d 190, 196 (1990)</a> (&quot;<em>A prosecutor is not necessarily ineligible because he does not like the defendant.</em>&quot;).</p>

criminal-law common-law witnesses rules-of-evidence