By Joshua Wood
A laboratory reported negative gunshot residue tests. The prosecution nevertheless asked the jury to use particles found in those tests to identify the shooter.
In Commonwealth v. Williams, SJC-12702, decided September 22, 2026, the Massachusetts Supreme Judicial Court held that the Commonwealth had not established a reliable scientific basis for that argument. The court vacated Williams’s first-degree murder conviction and ordered a new trial.
The decision is important because scientific evidence can sound more conclusive in a courtroom than it is. Before the prosecution asks a jury to draw a conclusion from a test, it must establish that the science reliably supports that conclusion.
The shooting and the disputed identification
The case arose from a shooting during a parade on Blue Hill Avenue in Dorchester on August 23, 2014. Two bystanders were struck. Dawn Jaffier was killed, and Lealah Fulton was injured.
The Commonwealth accused Keith Williams of firing the shots. Its case included substantial circumstantial evidence: a witness saw Williams dispose of a revolver shortly after the shooting, and ballistic testing linked that weapon to both victims.
But no witness positively identified Williams as the shooter. Witness descriptions differed, and a defense witness described clothing consistent with one of Williams’s companions. DNA and fingerprint testing of the revolver was inconclusive. The identity of the shooter remained the central dispute at trial.
Why the gunshot residue tests were negative
Gunshot residue, often called GSR, consists of particles released when a firearm is discharged. As the expert explained in Williams, a person can acquire those particles by firing a gun, handling a firearm, being near a discharge, or coming into contact with a contaminated person or surface.
Under the testing standards described at trial, a positive result required at least three qualifying particles in a single sample. Particles from separate tests could not be added together to reach that threshold.
The laboratory found one particle in a sample from Williams’s hands and another in a sample from his T-shirt. No particles were found in the hand samples from his two companions. Every gunshot residue test was negative.
The three-particle requirement served a scientific purpose. The expert testified that it accounted, in part, for contamination and the need to interpret results accurately. He agreed that there was “nothing to be drawn from” these negative results. His reports likewise stated that the results supported no conclusion about whether the individuals had fired a gun, been near a discharge, or contacted something bearing residue.
Contamination was a live issue. The expert acknowledged that residue can persist on handcuffs and surfaces in police vehicles and stations. Police collected the hand samples more than three and one-half hours after the shooting, after the men had been handcuffed and transported. The defense argued that transfer could explain the particles. The court did not find that contamination had actually occurred.
The prosecution had to establish what the particles could prove
Detecting a particle and establishing that a person fired a gun are separate propositions. The Commonwealth had to show a reliable scientific basis for connecting them in this case.
Massachusetts judges serve as gatekeepers for expert testimony. Under the reliability principles discussed in Williams, including the Daubert-Lanigan standard, the party offering expert evidence must establish that the method is reliable and that its application to the particular issue is reliable. The judge must make that threshold determination before the evidence goes to the jury.
The Commonwealth failed to do that. Its own expert testified that no conclusion could be drawn from the negative results, and the prosecution offered no scientific basis for treating the underlying particles as evidence that Williams fired the gun.
The prosecution argued that the defense could address its concerns through cross-examination and leave the jury to decide what weight to give the particles. The SJC rejected that approach on this record. Cross-examination did not relieve the Commonwealth of its initial obligation to establish reliability.
The distinction became particularly clear in closing argument. The prosecutor told jurors that the laboratory’s threshold was not their standard and urged them to use the particles to identify Williams as the shooter. Leaving that choice to the jury did not cure the missing scientific foundation.
What Williams changes for gunshot residue evidence
The Commonwealth relied on an earlier decision, Commonwealth v. Johnson, 463 Mass. 95 (2012), which had discussed an inference of culpability from particles found below the threshold for a positive result.
Williams clarified the limits of Johnson. The earlier case did not establish that particles below a laboratory’s cutoff, standing alone and without a showing of reliability, necessarily support an inference that someone fired a gun. The SJC expressly disavowed any suggestion otherwise.
The court also made clear that below-threshold results are not categorically inadmissible. Their admissibility depends on the scientific foundation offered and the inference the jury is being asked to draw. A result can provide reliable information without being definitive. In Williams, the Commonwealth had not established even that limited basis for its proposed use of the particles.
Why the error required a new trial
The disputed evidence featured prominently in the prosecution’s opening statement and closing argument. The other evidence identifying Williams as the shooter was not overwhelming. The SJC could not conclude that the error had no influence on the jury or only a slight effect.
The court therefore ordered a new trial on the murder, armed assault with intent to murder, and assault and battery by means of a dangerous weapon charges.
It separately vacated the conviction for carrying a firearm without a license because the jury had not been instructed that the Commonwealth had to prove Williams lacked a valid license. That conviction was set aside for a different reason.
Williams may still be retried for first-degree murder. The court rejected his argument that the evidence of deliberate premeditation was insufficient. The decision gave him a new trial; it did not acquit him.
What the decision means for a criminal defense
For a defense lawyer, Williams directs attention to the precise conclusion the prosecution wants the jury to reach. It is not enough to ask whether a laboratory can reliably detect a substance. Counsel must also examine what the result reliably says about the alleged crime.
That review should include the laboratory’s report, its interpretive thresholds, the underlying results, and the circumstances of collection. A report’s limitations deserve the same attention as its findings.
Where the proposed inference lacks a reliable foundation, counsel should raise a focused challenge to admissibility before trial and request a Daubert-Lanigan hearing where appropriate. Williams illustrates why waiting to explain the problem through cross-examination may leave the jury with scientific evidence it should never have heard for that purpose.
Q and A
Can a negative gunshot residue test be used against a defendant in Massachusetts?
Particles underlying a negative result may be admissible if the prosecution establishes that they reliably support the particular inference it proposes. Williams does not impose a blanket ban. It requires a sufficient scientific foundation for that use of the evidence.
Does a negative gunshot residue test prove someone did not fire a gun?
No. The expert in Williams testified that no conclusion could be drawn from these negative results about whether someone had fired a firearm. The decision does not turn a negative test into proof of innocence.
Does gunshot residue on someone’s hands prove that person was the shooter?
No. The testimony in Williams identified several possible ways residue could reach a person’s hands, including handling a firearm, being near a discharge, and transfer from a contaminated surface. The significance of a finding depends on the test, the circumstances, and a reliable interpretation.
Can particles from different samples be combined to produce a positive result?
Under the protocol described in Williams, no. A positive result required at least three qualifying particles in one sample. Individual particles from separate tests could not be added together to meet that requirement.
What is a Daubert-Lanigan challenge?
It is a challenge to the reliability of proposed expert evidence. It can address the method itself or whether that method reliably supports the particular conclusion offered in the case. A separate evidentiary hearing is not required in every case.
Did the SJC dismiss the charges against Keith Williams?
No. The court vacated his convictions and returned the case to the Superior Court for further proceedings. It expressly permitted a retrial on first-degree murder because the evidence of deliberate premeditation was sufficient.
Conclusion
Commonwealth v. Williams requires careful attention to what forensic evidence can actually establish. A particle count may be accurate while the conclusion the prosecution draws from it remains unsupported.
Before that conclusion reaches a jury, the Commonwealth must establish the necessary scientific foundation. In a case where identity is disputed, that requirement can determine whether the jury hears reliable evidence or an accusation given the appearance of scientific support.
If you or a family member is facing criminal charges in Massachusetts, call Benzaken, Sheehan & Wood, LLP to discuss the case. We can review the evidence, assess whether it reliably supports the prosecution’s claims, and explain your options. You should understand what the Commonwealth can actually prove before making decisions about your defense.