For the third time in less than two years, a bespectacled young woman took the stand in a Boston courthouse yesterday and haltingly described how a tall stranger with a goatee and alcohol on his breath entered her bedroom in Dorchester in 2001 and raped her.
At two earlier trials, Suffolk prosecutors contended that Darrin Fernandez, a 31-year-old convicted rapist, was the intruder on the basis of seemingly unimpeachable evidence: DNA recovered from a blue pillowcase matched his genetic profile.
But both juries failed to reach a verdict for an unusual reason: The genetic material could also have come from his identical twin.
As Fernandez's third trial started, prosecutors began with a big advantage they lacked in the prior trials. Suffolk Superior Court Judge Raymond J. Brassard allowed them to present evidence that Fernandez, a one-time house painter, had committed four similar break-ins in the neighborhood over an 11-month period and had been convicted of rape in one of those cases. The ruling, some legal specialists said, could make the difference in the verdict this time.
''In a case like this where a jury has deadlocked, almost anything can tip the balance," said Marc G. Perlin, an associate dean at Suffolk University Law School.
Under state law, juries are usually barred from hearing evidence that a defendant has committed other crimes, because it is prejudicial. But Assistant District Attorney David A. Deakin successfully argued that a jury was entitled to hear the evidence because it refuted the defendant's theory that Fernandez's identical twin, Damien Fernandez, could have been the source of the DNA. Identical twins have the same DNA.
Brassard agreed in a ruling last week, saying that the rape Aug. 26, 2000, of a young woman asleep in her parents' home on Hecla Street in Dorchester -- for which Darrin Fernandez is serving a 10- to 15-year sentence in state prison -- was ''strikingly similar" to the one on Peverell Street, in which Fernandez is on trial now.
The Hecla Street victim, whom prosecutors had been reluctant to call at Fernandez's prior two trials because they did not want to cause her any more anguish, has agreed to take the stand.
Robert J. Zanello, who is defending Darrin Fernandez for the third time, opposed the request to present the additional evidence. But he said he hoped the possibility that the DNA could have come from Damien Fernandez would still prevent the jury from convicting his client.
The rape on Peverell Street occurred shortly after midnight on April 27, 2001, when a man climbed a fire escape leading to a second-story porch of a house where the victim, now 34, lived with several housemates.
The woman, who now lives in Illinois, told the jury that something woke her, and she saw a man standing at the foot of her bed in the darkness. Initially, she testified, thought it might be one of her housemates. But then she realized that it was no one she knew.
Darrin Fernandez was charged in the rapes on Peverell and Hecla streets after police arrested him in July 2001 after he allegedly tried to break into an apartment on Stonehurst Street in Dorchester.
Jonathan Saltzman can be reached at email@example.com.