The “No Bolstering Rule” is a rule that prohibits the use of hearsay evidence to the effect that a non-testifying person agreed with the testifying witness about the truth of what the witness has stated during direct examination. The rule states, essentially, that a witness cannot bolster his own testimony with confirmatory statements made out-of-court by another person when the testifier has not yet been impeached.  It is an integral part of the prohibition against the evidentiary use of most hearsay evidence. 

The rule against the use of hearsay evidence is peculiar to adversary system jurisdictions  (United States, Canada, the United Kingdom, and other Commonwealth countries). The rule against hearsay has no direct equivalent in civil law countries. Hearsay evidence comprises those assertions or declarations of a non-testifying person which are offered to prove the truth of the testifying person’s assertions. The concept applies to lay as well as expert witnesses in both civil and criminal cases.

When dealing with fingerprint expert witness testimony, the “no bolstering” rule prohibits one examiner from making a statement of fact or of stating an opinion and following that up with the assertion that another, non-testifying person, agrees with that fact or opinion, or that this non-testifying person has the same view. Thus, one expert cannot state, “This is my conclusion, and Ms. X has confirmed that my conclusion is correct.” Or, “this is my opinion, and so-and-so agrees that I was right.” Or, “several other people have also seen this evidence and they all came to the same conclusion.”  Or,” everybody knows that it is so.” Or, “ten other people said the same thing.”

None of the above statements would be admissible if a proper objection is raised, because the “declarants”   –   the persons who made the out-of-court statement(s)   –   are not available to be cross-examined as to the assertions’ veracity, accuracy, or reliability. [See also, “Hearsay Evidence” in Wiley Encyclopedia of Forensic Science (Jamieson A and Moenssens A.A. eds.) 2009 [3] 1465 for a more extensive explanation of the hearsay rule as applied to forensic scientists.]

The “No Bolstering Rule” requires fingerprint examiners to also refrain from volunteering information about the outcome of a verification after having explained what each step of the ACE-V process, including the verification step, requires.

A few recent court decisions, have applied the “no bolstering” rule in cases wherein fingerprint examiners were asked, after they explained the various steps involved in the ACE-V process (including the requirement of a Verification), whether the “verifying examiner” agreed with the testifying examiner’s conclusion, and the examiner responds affirmatively. The same result – reversal of a conviction  –   is likely to occur if the testifying examiner were to volunteer such information on direct examination without being asked that question.

Note that it is entirely proper to explain during testimony what each step of the ACE-V process entails. Do not, however, violate the “no bolstering” rule by volunteering that the verifying examiner has reached the same conclusion. Since the verifier is not on the stand, he/she cannot be cross-examined on the correctness of that statement; the statement therefore violates the rule against using inadmissible hearsay evidence against a defendant.

“No Bolstering”  and the prohibition against the use of most forms of hearsay evidence has its origin in the judge’s function to insure that jurors are not misled or confused by evidence that cannot be examined or challenged, and may therefore potentially also be unreliable. In the United States, the rule is part and parcel of the constitutional right to cross-examine all witnesses. The rule against the use of hearsay evidence is somewhat archaic, and certainly very technical. What’s more, there exist a slew of exceptions to the rule against hearsay  –   situations where statements of non-testifying persons can nevertheless be used in evidence   –   but it is well understood by most legal professionals. 

There are a few instances where the “no bolstering” rule may gave way on redirect if the cross-examiner sought to impeach the testifying expert by allegations that he/she has recently fabricated or changed his/her opinion. This would be one case wherein the examiner may thereafter be asked whether, at the time he/she had first formulated the opinion, other examiners had agreed with it. This, again, is a technical concept that would apply only after cross-examination of the testifying expert by the defense attorney. It is a situation that comes up very seldom, and therefore less likely to cause problems for a fingerprint examiner.