Jurors probably would have spared Boston Marathon bomber Dzhokhar Tsarnaev the death penalty during his 2015 trial had they learned that his older brother and accomplice allegedly killed three people in Waltham less than two years before the blasts, said a brief filed by the National Association of Criminal Defense Lawyers.
Its amicus brief was submitted to the US Court of Appeals for the First Circuit in Boston, where Tsarnaev is challenging his death sentence for his role in the April 2013 bombings, which killed three people and wounded hundreds more. Tsarnaev and his older brother, Tamerlan, also killed an MIT police officer while they were on the run.
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In their filing on Wednesday, the defense lawyers group said the jury that weighed Dzhokhar Tsarnaev’s fate should have been informed of Tamerlan’s “history of brutality and proclivity for planning and coordinating acts of homicidal violence — matters which went to the heart of defense arguments about relative culpability during the penalty phase of the trial.”
That was an apparent reference to Tamerlan’s alleged involvement in the slayings of three men in September 2011 in Waltham. Tamerlan was killed four days after the Marathon blasts in a confrontation with police in Watertown.
The judge who presided over Dzhokhar’s high-profile trial in 2015 barred his lawyers from telling jurors about his brother’s alleged link to the 2011 slayings. Weeks after the 2013 bombings, another man allegedly confessed to the authorities that he had carried out the 2011 triple murder with Tamerlan.
That man, Ibragim Todashev, was killed in Orlando by investigators after he allegedly attacked them during an interview.
In Wednesday’s filing, the defense lawyers association said jurors in Dzhokhar Tsarnaev’s trial didn’t have the full picture of Tamerlan’s violent sway over people close to him.
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“Here, the jury was provided an incomplete portrayal of Dzhokhar Tsarnaev’s role in the offense: the district court precluded critical evidence that Tamerlan Tsarnaev had committed horrific acts of violence, and had influenced another person to commit those crimes with him,” the filing said. “This Court should join those around the country vacating death sentences under similar circumstances in recognition of the likelihood that at least one juror will reach a different conclusion when permitted to see the complete picture of Dzhokhar Tsarnaev’s less culpable role.”
No one has ever been charged in the Waltham triple slaying.
Federal prosecutors hadn’t responded to the filing as of Thursday morning. The defense lawyers group submitted the document as a proposed amicus brief. It was attached to a motion for permission to file the document as part of the official record.
In the brief, the lawyers also asserted that juries frequently hand down life sentences to defendants convicted of even the most heinous killings, provided there’s compelling mitigating evidence in the murderer’s favor.
The brief cited capital cases that resulted in life sentences, including that of Zacarias Moussaoui, the infamous defendant known as the “20th hijacker” in the 9/11 terror attacks.
“During the penalty phase of Moussaoui’s trial, jurors were shown evidence that powerfully revived the shock and terror of September 11, 2001,” the filing said. “ . . . Moussaoui took the witness stand to express his ‘delight’ at hearing these accounts of human suffering. Addressing survivors who had appeared in court, Moussaoui told the jury he regretted that they had lived and that he remained determined to kill Americans, even in prison.”
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But not even Moussaoui’s “delight in the carnage” wrought by the deadliest terror attack on US soil convinced jurors to condemn him to death, the association said.
“Instead, jurors were persuaded by mitigating evidence that Moussaoui had a difficult childhood, had spent time in orphanages, was not a leader of the 9/11 attacks, and was primarily involved in plotting subsequent attacks,” the document said. “A comprehensive mitigation case was able to persuade jurors to spare the life of a man who bragged about his ‘delight’ at the vast death and destruction that he helped bring about, who mocked survivors of his terror, and who vowed to kill more if able.”
The lawyers added that no case “has been too aggravated, grotesque, or disturbing to prevent courts from vacating death sentences when they identify errors affecting the integrity of capital proceedings.”
Tsarnaev, 25, is incarcerated at a federal supermax prison in Colorado. Moussaoui is serving a life term at the same prison.
A hearing date hasn’t been set for oral arguments in Tsarnaev’s appeal in Boston.
Separately Thursday, a nonprofit named for Sean Collier, the MIT officer fatally shot by the Tsarnaev brothers, asked the public to remember the young officer.
“Please take a moment to remember Sean today, on what would have been his 33rd birthday,” said the Officer Sean A. Collier Memorial Fund in a Twitter message.
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The fund’s sentiments were echoed by the MIT Police Department.
“Let’s remember Sean on his birthday by doing small acts of kindness in his memory today,” the department tweeted. “Gone but never forgotten. #CollierStrong.”
Travis Andersen can be reached at travis.andersen@globe.com. Follow him on Twitter @TAGlobe.