New York Federal Criminal Practice Blog
October 29, 2008

SDNY Judge Rules that Ballistics Expert May Not Testify that Ballistics is a Science or that He Reached his Conclusions with any Degree of Certainty

Scientific testimony has an inexorable way of assuming central importance at a trial.  In the world of CSI, as this blog has noted in the past, see here, jurors crave the objective certainty that scientific evidence promises.  But as Judge Rakoff sums up the conundrum in United States v. Glynn, 2008 WL 4293317 (S.D.N.Y. September 22, 2008), while juries are supposed to evaluate an expert’s testimony and decide what weight to give it, they “are necessarily handicapped in doing so by their own lack of expertise.”  In other words, the blind cannot lead the blind.  It falls on the trial judge to ensure the jury isn’t bamboozled by unreliable expert testimony.  And admirably stepping up to his gatekeeper plate, Judge Rakoff held in Glynn, following a Daubert hearing, that the government’s ballistics expert could not testify that ballistics is a science, nor could he testify that he reached his conclusions with any degree of certainty.  Rather, he could simply “give an opinion that it was at least ‘more likely than not’ that the bullet and casings came from the guns in question.”


Quite simply, ballistics analysis may have the pretensions of science, but it does not have “sufficient rigor to be received as science,” Judge Rakoff concludes, examining some recent district court cases from Massachusetts and California, as well as academic literature on the subject. 

Firearm analysis “rests on the twin assumptions that the surface contours of every gun are unique and that, every time that gun is fired, some of those unique markings, along with markings caused by the act of firing itself, are transferred to the shell casing and bullet, leaving distinctive patterns on each of them.”  Even in an era of mass production of firearms, “the gun manufacturing process never operates identically in any given case, and therefore causes differences between any two guns that, while tiny, may still be detected by use of such techniques as the comparison microscope.”  Of course, such comparisons are necessarily subjective, and the reliability of ballistics analysis is further compromised by the absence of “defining standards to a degree that exceeds most other kinds of forensic expertise” like, for example, fingerprint analysis.  In addition, “real-life conditions rarely allow for perfect comparisons” – bullets and/or shell casings recovered from the crime scene may be damaged; a gun barrel may itself change slightly with each firing; casings may be affected by an irregular firing or materials they hit against; and the instruments used to compare the samples have their own distorting effects.

Nevertheless, Judge Rakoff concludes that ballistics analysis “has garnered sufficient empirical support as to warrant its admissibility.”  After all, evidence need not meet an “exalted level of certainty” to be admissible; it must simply “make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence” (quoting Fed.R.Civ.P. 401).  Hence his decision to permit the ballistics examiner to testify in the case, with the limitation that his conclusions may only be couched in the “more likely than not” language, and thus not “overstat[e] the capacity of the methodology to ascertain matches.”


This decision is important not just for cases involving ballistics, but any case involving expert testimony, particularly where that expert evidence may relate to a disputed fact and may take on crucial significance at the trial.  It shouldn’t be forgotten that for decades, ballistics testimony was accepted without question in federal courts.  Glynn is a reminder that under the Supreme Court’s decision in Daubert, all areas of forensic “science” should be subject to careful scrutiny and re-evaluation, especially in light of developing scholarship that may cast doubt on their reliability. 

And the next step is to develop arguments for trial and appellate courts challenging the admission of “expert” testimony that something is “more likely than not” to be true.  One could argue, for example, that the minimal probity of such evidence cannot outweigh the prejudice that the jury may assign it undue importance, or that it risks lowering the government’s burden of proof.

Lawyers: Davide Ruhnke and Michael Young (for the defendant) and AUSA Jessica Masella.

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