The Court of in Williams v. U.S., decided on June 27, 2019, reiterated the legal standard for admissibility and reliability of the ballistic scientific evidence.

Williams was convicted of felony murder and one of key pieces of evidence against him was a testimony of the ballistic expert who had matched the toolmarks of a weapon found in the defendant’s home against the bullet shells found at the crime scene.  The expert at trial had testified with certainty that the ballistic imaging was a 100 percent match.

The Court of Appeals held that there was a lack of scientific data to be able to conclude with a 100 percent certainty that the ballistic imagining matched and thus admissibility of the expert testimony was an error however not a reversible error.

The central analysis by the appellate court was whether firearms-related toolmarks are unique: specifically, whether a particular set of toolmarks can be shown to come from one weapon to the exclusion of all others.  There is no data-based foundation for such pronouncement and with any certainty.

Moreover, not enough is known about the variabilities among individual tools and guns or how much similarity is necessary for a given level of confidence in the result.

Thus, firearms and toolmark expert may not give an unqualified opinion, or testify with absolute certainty and based on ballistics pattern comparison matching a fatal shot that was fired from one firearm to the exclusion of all other firearms.

Such experts may offer an opinion that a bullet or shell casing was fired by a particular firearm, but it does not permit them to do so with absolute or 100% certainty.

Because the ballistic expert had testified to being 100 percent certain and that there was no doubt as to there being a match between the bullet and the gun casing – such evidence should be excluded.

The scientific testimony or evidence admitted not only needs to be relevant, but even more importantly reliable.

In order for the Court to reverse a conviction though the Court must determine whether there was:

• An error, and
• Was the error material and affected substantial rights.

Here, clearly the admission of testimony was an error however overall it did not affect substantial rights of the defendant as there was sufficient independent evidence of the crime.  There was dispositive finger print evidence, partial confession through a witness, and several other circumstantial evidence that together could support the guilty verdict.

For an error to affect substantial rights the defendant must show reasonable probability of a different outcome but for the error.   There must be more than a mere possibility of prejudice, the error must in fact undermines confidence in the trial’s outcome.

That is, in reviewing the record as a whole, the Court held that Williams could not show there was a reasonable probability that the jury might have reached a different conclusion had the trial court properly excluded the firearms and toolmark examiner’s opinion testimony which unqualifiedly identified the gun found in Mr. Williams’s apartment as the murder weapon.

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