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Machines and human witnesses

By Richard D. Friedman

Paul Vinegrad has posed a question to me as a comment to an ealrier post. It?s sufficiently interesting that I?ll answer it here. Paul?s question:

Prof. Friedman, your thoughts on the following hypothetical would be illuminating:

Cop arrests suspect for DUI. Cop takes suspect's blood sample to government run lab. Cop watches as analyst places blood sample in gas chromatograph. Gas chromatograph prints out result of .21 BAC. Cop takes print out and leaves.

At trial, Cop describes this sequence of events. Cop identifies print out. Print out is marked as an exhibit and introduced into evidence to prove defendant's BAC was .21. Cop does not offer any opinion on accuracy/reliability of print out.

Did any human "witness" make a "statement" (testimonial or otherwise) that defendant's BAC was .21?

My answer is that, with one caveat discussed below, there is no human witness that the BAC is .21. What we have is a witness to a process that generated the identified piece of paper.

If instead of this test, it were a simple litmus paper test, and the witness identifies a particular piece of red litmus paper as the one that was dipped in a particular solution, and says it is now the color that it was after it was dipped in, I don?t think there?s yet been an assertion by a human witness that the solution was acidic. One can infer that proposition by understanding the processes that led to the red color.

Now of course the case Paul presents is different in that humans presumably created and calibrated the machine. But presumably that all happened before the particular testing. Even if one could discern a human assertion there, it?s harder to discern an assertion about the particular sample, and I think Melendez-Diaz suggests pretty strongly, for better or worse, that an assertion at this point wouldn?t be considered testimonial.

The caveat is that it is theoretically possible that somebody purposely set the machine so that it would report a BAC of .21. If so, I?d say that?s an assertion, made by a human through a machine ? just as one might use a machine to broadcast his voice. But I think the burden would be on the defendant to produce evidence of this kind of manipulation.

The most difficult question here is one of relevance, or probative value: Is there enough of a basis for the trier of fact to conclude that because the piece of paper says .21 that in fact the blood alcohol content of the sample tested was .21? Compare this to a witness who says that when a robbery occurred the digital clock on the top floor of the bank said it was 1:45. In a case like that, I don?t think we?d demand proof as a precondition to admissibility that the clock was accurate, at least if the evidence is significant even without pinpoint accuracy; the jury could probably infer that the clock was likely reasonably accurate or it would?ve been corrected. (Though in my town there is a prominent digital clock, right where cars pull off a main road into one of the malls, that has been slow by about four minutes for many years). Of course, the prosecution might choose to supply such proof on its own initiative, and the defense may challenge the accuracy of the clock. But in this case, assuming the cop isn?t familiar with the machine from other encounters, is there enough of a basis for the trier of fact to infer that the machine is reasonably accurate? I don?t know. Certainly the prosecution would be better off presenting proof of accuracy. But I don?t think failure to do so is a confrontation problem.

Full post as published by The Confrontation Blog on January 20, 2011 (boomark / email).