Massachusetts SJC Rejects New Trial for Defendant Convicted of Murder: No Relief Based on New Eyewitness Identification Science
On May 5, 2025, the Massachusetts Supreme Judicial Court (SJC) issued an important ruling in Commonwealth v. Thomas Mercado, SJC-13548, holding that new scientific research on the unreliability of eyewitness identification did not entitle a defendant convicted of first-degree murder to a new trial.
The decision is a critical clarification of how Massachusetts courts will handle post-conviction claims based on advances in cognitive science and psychology. It also illustrates the steep legal hurdles defendants face when seeking a new trial based on evolving scientific insights—even when those insights touch on one of the most controversial forms of evidence in the courtroom: eyewitness testimony.
Background: The 2006 Murder and Conviction
The case stretches back nearly two decades. In February 2006, Jeanette Martinez and her friend Corrin Cripps were in Martinez’s second-floor apartment in an urban multi-family home, using cocaine. Cripps visited the neighboring apartment, where several men, including the eventual victim, were packaging cocaine. When she returned, two new men—one identified as “Pelon” and the other as the defendant, Thomas Mercado—arrived at Martinez’s apartment.
Soon after, Cripps and Martinez overheard Mercado and Pelon discussing a plan to “kill the guy” next door. Shortly after that, Cripps, Martinez, and others heard gunshots in the hallway. Martinez looked through the peephole and saw a hooded man, whom she later identified as Mercado, firing a gun.
The victim, who had been shot six times, died from his injuries. Mercado quickly fled Massachusetts and was later arrested in Puerto Rico, where he provided police with a false name.
Mercado was tried and convicted of first-degree murder in 2009. His conviction was affirmed by the SJC in 2013. He filed a first motion for a new trial based on ineffective assistance of counsel, which was denied.
The New Motion for a New Trial: Advances in Eyewitness Science
In November 2022, more than a decade after his original conviction, Mercado filed a second motion for a new trial. This time, he argued that newly discovered scientific research on the unreliability of eyewitness identifications—research that had not been available at the time of his trial—cast serious doubt on the fairness of his conviction.
Mercado relied on expert testimony from Dr. Nancy Franklin, a recognized authority on human memory and eyewitness reliability, who detailed significant advancements in the field since Mercado’s 2009 trial. This included studies on:
The fallibility of stranger identifications,
The effects of stress and intoxication on memory,
The risks of multiple witnesses reinforcing mistaken identifications, and
The danger of suggestive police procedures.
Mercado’s motion focused on the three eyewitnesses at his trial:
Cripps (who admitted she was using crack cocaine at the time),
Martinez (who was also under the influence), and
Michael Gomes (who failed to initially identify Mercado in a photo array).
He argued that the new scientific research would have raised critical doubts for the jury about the accuracy of these identifications.
The Legal Standard: High Bar for a New Trial
Under Massachusetts law, a motion for a new trial based on new evidence must show two things:
That the evidence is newly discovered—meaning it was unknown and not reasonably discoverable at the time of trial; and
That the absence of this evidence at the original trial was prejudicial, meaning it probably would have been a real factor in the jury’s deliberations and casts real doubt on the justice of the conviction.
The Superior Court judge who heard Mercado’s motion (who was not the original trial judge) ruled against him, finding that although the scientific research was indeed newly discovered, it was not prejudicial in this case.
The judge concluded that the jury would not likely have reached a different verdict even if they had heard this new research.
The SJC’s Ruling: Affirming the Denial
On appeal, the SJC affirmed the denial of a new trial, laying out several key reasons.
1️⃣ The Research Applied to Only One Witness
The Court found that the new scientific evidence on stranger identifications applied only to one of the three eyewitnesses: Michael Gomes.
Gomes did not know Mercado before the shooting and initially failed to identify him from a photo array.
However, trial counsel had already impeached Gomes at trial over this failure, meaning the jury was well aware of the issue.
In contrast, Cripps and Martinez were familiar with Mercado—they had spent significant time with him in the hours leading up to the shooting. Scientific studies on stranger misidentifications didn’t apply to familiar identifications, and thus, the new research would have carried little weight against their testimony.
2️⃣ There Was Additional Evidence of Guilt
The SJC emphasized that the case did not rest solely on eyewitness identifications.
There was powerful circumstantial evidence as well:
Mercado was overheard planning to “kill the guy.”
He fled Massachusetts immediately after the shooting and assumed a false identity in Puerto Rico, which the Court described as consciousness of guilt.
The Court concluded that the jury had multiple, independent reasons to convict, beyond the eyewitness testimony.
3️⃣ The Jury Was Already Alerted to the Witnesses’ Weaknesses
At trial, defense counsel had already highlighted:
That Gomes initially identified someone else in the photo array,
That Cripps and Martinez had been using crack cocaine the night of the murder, raising questions about their perceptions.
Thus, the jury was already in a position to critically evaluate the weaknesses in the Commonwealth’s eyewitness evidence.
4️⃣ Comparison to Recent Precedent (Commonwealth v. Gaines)
Mercado’s defense team relied heavily on the SJC’s 2024 decision in Commonwealth v. Gaines, where the Court ordered a new trial based on newly discovered eyewitness identification science. But the SJC pointed out critical differences.
In Gaines, there was only one eyewitness, who identified a stranger under suggestive conditions, and there was no physical or circumstantial evidence connecting the defendant to the crime. Here, by contrast:
There were multiple eyewitnesses,
There was additional corroborating evidence, and
The witnesses’ relationships to Mercado undercut the relevance of the stranger misidentification research.
What Defense Lawyers Need to Know
The Mercado decision has important lessons for Massachusetts criminal defense attorneys, especially those handling post-conviction cases.
✅ Advances in eyewitness science matter—but they’re not a golden ticket.
New research can be powerful, but only if it applies to the specific facts of the case and significantly undermines the jury’s original basis for conviction.
✅ Familiarity matters.
Scientific studies on the unreliability of stranger identifications carry little weight when the witnesses personally knew the defendant.
✅ Cumulative evidence counts.
Where there is strong circumstantial or corroborating evidence, appellate courts are less likely to view eyewitness weaknesses as outcome-determinative.
✅ Preservation is key.
While scientific advances may not have been available at the time of trial, Massachusetts courts require that defense teams make every reasonable effort to challenge shaky evidence—including cross-examining witnesses on issues like intoxication, lighting conditions, and prior failures to identify.
Broader Implications
The Mercado ruling underscores a broader challenge for the criminal defense bar: how to leverage scientific advances in memory, perception, and identification in a legal system that prizes finality.
While the SJC has shown in recent years that it is open to reexamining shaky convictions in the right circumstances, it also makes clear that:
Not every case involving eyewitness testimony qualifies, and
Not every new piece of science will warrant reopening old trials.
Defense lawyers must carefully build records, tailor expert testimony, and show not only that the science is new, but that it would have made a real difference.
Conclusion
In Commonwealth v. Mercado, the Massachusetts Supreme Judicial Court drew a clear line: while new eyewitness identification research is significant, it will not justify a new trial unless it strikes at the heart of the original conviction.
For Massachusetts criminal defense practitioners, the case offers both a cautionary tale and a roadmap: advances in science are powerful tools—but they must be deployed with precision, applied thoughtfully to the facts, and framed in a way that shows how they would actually change the outcome.
As the science of human memory continues to evolve, defense attorneys must stay sharp, stay current, and stay ready—not just to know the latest studies, but to show why they matter.