Underscoring the limitations of DNA evidence, a Suffolk County jury said yesterday that it was deadlocked over whether a man raped a woman in Dorchester in 2001, given that his identical twin has the same DNA, prompting the judge to declare a mistrial.
Before the trial began, the lawyer for Darrin Fernandez asked the judge to postpone the case so that sophisticated DNA testing that can detect differences in the DNA of identical twins could be carried out, a process that a Boston University professor said could take two years.
But the judge refused to delay the trial. And yesterday, after deliberating the fate of Fernandez for about 24 hours over four days, longer than the trial itself, the jury sent Superior Court Judge Elizabeth B. Donovan a note saying that it had been at an impasse since Friday afternoon and could not reach a verdict.
Donovan, who had received a similar note Monday, asked the jurors to vote on whether to quit. When the jury sent back a note indicating it couldn't even reach a consensus on that -- the vote was 6 to 6 -- she declared a mistrial.
Afterward, a juror, Matthew Dullea, said that he and eight other jurors had voted to convict Fernandez, but that three insisted he be acquitted because DNA evidence at the rape scene could have also come from his identical twin, Damien Fernandez.
Dullea, 31, who is an identical twin himself, said emotions ran high as the jurors debated the possibility that Damien Fernandez was the rapist. But Dullea said he had no doubts that the state prosecuted the right man.
''Just because he's an identical twin doesn't give him a pass to do what he feels like," said Dullea, who, like the other jurors, had been unaware that Fernandez was already serving a long prison sentence for a rape conviction. During that trial he had used the same defense: maybe his brother did it.
The jury deliberations were emotional, Dullea said, with jurors raising their voices and slapping the table. One juror was a scientist who was knowledgeable about DNA technology, said Dullea, who declined to specify whether that juror wanted to convict or acquit.
''Emotions were running high because of the nature of the crime and because everybody's heart went out to the victim," Dullea said. ''The fact that the DNA matches both identical twins created some doubt in all of our minds, but that doubt weighed more for some and much less for others."
In recent years, DNA evidence has become the gold standard for linking suspects to crimes and for exonerating those wrongly convicted. But under extraordinary circumstances, such as a case involving identical twins, it has its limitations. Since identical twins come from the same fertilized egg, which splits, they have the same DNA.
At a hearing last month before the Fernandez trial began, a Boston University professor of biomedical engineering, Cassandra L. Smith, testified that advanced technology can detect differences in the DNA of identical twins if the genetic material has mutated.
Mutations can occur when cells divide as the human embryo grows. But locating the mutations is costly and time-consuming, and the changes may not be present in all types of tissue.
But Smith said the tests could take two years or more to carry out, prompting Donovan to reject a request by Fernandez's lawyer to delay the trial until testing could take place.
Fernandez, 29, is already serving a 10- to 15-year sentence in state prison after being convicted last year of climbing through an open window around 1:35 a.m. on Aug. 26, 2000, and raping a young woman asleep in her parents' home on Hecla Street in Dorchester. Yesterday, a jury was unable to reach a verdict about whether he had also raped a woman after entering a Peverell Street house around midnight on April 27, 2001, in the same neighborhood.
In both trials, a criminalist for Boston police testified that DNA evidence recovered at the rape scenes could have come from either Darrin Fernandez or his identical twin, Damien. The first jury convicted Darrin Fernandez after the victim identified him in the courtroom as her attacker, said Fernandez's lawyer, Robert J. Zanello. The victim testified that she recalled seeing a tattoo that read ''twinz" on her attacker's left arm. Fernandez has such a tattoo, but it is on his right arm.
Damien Fernandez, who has no ''twinz" tattoo, testified that he was living in Worcester when the earlier rape occurred.
Damien Fernandez testified again in the second trial, saying he was living in Brockton at the time of the second rape, Zanello said. But the rape victim never identified Darrin Fernandez in the courtroom as her attacker and never mentioned seeing a tattoo.
Darrin Fernandez did not testify at either trial.
Suffolk District Attorney Daniel F. Conley said that he was disappointed in the verdict but that his office plans to retry the case. That would mean bringing the victim, who now lives in Illinois, back to Massacusetts again.
Darrin Fernandez was charged in both rapes after police arrested him in the summer of 2001 after he allegedly tried to break into an apartment on Stonehurst Street. He cut himself smashing a window, and investigators linked the DNA in blood found at the scene to DNA in semen recovered in the rape investigations.