EvidenceProf Blog

Editor: Colin Miller
Univ. of South Carolina School of Law

Monday, November 5, 2012

Where The Truth Lies: The Hearsay Problem With Lie Detector Evidence

I have been writing quite a bit about lie detector evidence recently and have been mainly focused upon the (un)reliability of such evidence. Until recently, I hadn't really thought about the hearsay implications of such evidence. But then I came upon The Significance (If Any) for the Federal Criminal Justice System of Advances in Lie Detector Technology, 80 Temp. L. Rev. 711 (2007), by past EvidenceProf guest blogger Jeff Bellin. In the piece, Professor Bellin makes a compelling case for much lie detector evidence being inadmissible under the rule against hearsay.

Federal Rule of Evidence 801(c) defines "hearsay" as 

a statement that:

(1) the declarant does not make while testifying at the current trial or hearing; and

(2) a party offers in evidence to prove the truth of the matter asserted in the statement.

In turn, Federal Rule of Evidence 802 deems hearsay statements inadmissible unless a hearsay exception applies.

So, let's say that (1) a criminal defendant "passes" a polygraph or fMRI test, or (2) some other defense or prosecution witness "passes" or "fails" one of these tests. As Professor Bellin notes

The most cogent evidentiary objection to scientifically valid expert lie detector testimony is that it is hearsay. This is because any proffer of lie detector evidence will include two distinct elements: (1) an out-of-court statement by the defendant or another witness, and (2) expert testimony that the out-of-court statement is true. Central to the proffer, then, is an out-of-court statement that gives every appearance of being offered for its truth--i.e., hearsay. In fact, considering that a simple hearsay objection has the potential to render the entire debate regarding the scientific reliability of lie detector evidence (past and present) moot, it is surprising how little analysis has been devoted to the subject


The hearsay problem arises in virtually any presentation of lie detector evidence due to the fact that all such evidence depends for its relevance on an effort to prove the truth of an underlying out-of-court witness statement. This problem is readily apparent when a defendant attempts to introduce an exculpatory statement through a lie detector expert--significantly, the very scenario where lie detection could provide the greatest service to the criminal justice system.

A defendant's out-of-court statement to a witness that he did not commit the charged crime is a classic example of inadmissible hearsay. As a general matter such evidence, when offered by the defense, falls squarely within the hearsay prohibition and cannot be admitted under any hearsay exception. This prohibition similarly applies when the defendant (or any witness) makes an out-of-court statement to a lie detector expert. The expert's in-court repetition of the test subject's out-of-court statement is hearsay and inadmissible. As the expert's opinion is only relevant to establish the potential truth of the subject's answers, the hearsay bar to revealing those answers to the jury renders the lie detector expert's testimony irrelevant and inadmissible.

Indeed, in the case in which a defendant is offering evidence that he passed a lie detector test,

not only is the defendant's statement during the lie detector examination offered for its truth, but in introducing the statement through what is essentially a "truth expert," the defense attempts to establish its substantive truth in two separate ways. First, in traditional fashion, the defendant's assertion concerning a fact at issue is presented to the jury. As the defendant's assertion is only relevant for its potential truth, this statement, like virtually all witness testimony, is offered by its proponent for that purpose. Second, the statement is presented as true in a more novel way, through expert opinion testimony that an application of lie detection technology supports a conclusion that the statement is truthful. In essence, the statement is offered as substantive evidence, and then because the truth of the statement is in doubt, the defense supports the inference that the statement is substantively true with expert testimony.

So, would a hearsay exception apply to such lie detector evidence? Professor Bellin argues that not typical hearsay exception applies and that the only possibility would be the residual exception contained in Federal Rule of Evidence 807, which states that

Under the following circumstances, a hearsay statement is not excluded by the rule against hearsay even if the statement is not specifically covered by a hearsay exception in Rule 803 or 804:  

(1) the statement has equivalent circumstantial guarantees of trustworthiness;  

(2) it is offered as evidence of a material fact;  

(3) it is more probative on the point for which it is offered than any other evidence that the proponent can obtain through reasonable efforts; and  

(4) admitting it will best serve the purposes of these rules and the interests of justice.

But, in the event that courts don't apply this extraordinary exception, there seems to be another obstacle that lie detector advocates have to clear.



| Permalink

TrackBack URL for this entry:


Listed below are links to weblogs that reference Where The Truth Lies: The Hearsay Problem With Lie Detector Evidence:


So, what's to stop someone from bringing a lie detector machine to court and use it while the person is on the witness stand so the judge/jury can see it first hand? I'm not persuaded in this case that "out-of-court" has anything to do with it because it's relatively easy to turn such out-of-count into "in court" statements.

Posted by: Daniel | Nov 5, 2012 3:03:13 PM

Daniel: That's true, but doing that would create its own set of problems. Here are three:

1. Attorneys like to know what their witnesses are going to say before they testify so that they can have their version of the case established before trial. I'm not sure that either side would want to take the risk of their key witness failing a lie detector test while on the witness stand.

2. Courts worry about jurors overvaluing lie detector results, and that is with those results simply being coldly discussed by the expert on the stand. Can you imagine what effect a live lie detector test in the courtroom would have on the jury.

3. Finally, I was discussing ecological validity that other day. I have to imagine that the false positive rate would spike when witnesses are in he courtroom, being watched by the judge, the jurors, and the media, and everything on the line.

Posted by: Colin Miller | Nov 6, 2012 3:14:28 AM

Post a comment