Federal prosecutors have identified a witness prepared to testify that Boston Marathon bombings suspect Dzhokhar Tsarnaev knew his older brother and alleged accomplice Tamerlan Tsarnaev participated in a 2011 triple murder outside Boston.

The disclosure was made by Dzhokhar Tsarnaev’s defense team in a federal court filinglate Friday, as part of a larger push by his attorneys to gain access to “discovery” evidence compiled by the federal government in its case against Tsarnaev for the April 2013 bombings that killed three and injured several hundred near the marathon’s finish line.

The Sept. 11, 2011, murders — which occurred in Waltham, Mass., a suburb of Boston — remain officially unsolved. But the murders, which were initially written off by local police as a drug deal gone bad, have become a plot point in the Boston bombings case amid evidence that Tamerlan Tsarnaev was involved. This is the first time there’s been a suggestion that his younger brother might have been aware of his alleged participation in the murders — which some have said, if solved, might have prevented the marathon attacks.

Tamerlan Tsarnaev, who was killed during a confrontation with police three days after the bombings when his brother ran over him with a car, was close friends with one of the Waltham victims: Brendan Mess, 25, a martial arts instructor who police say also dealt drugs on the side. But Tsarnaev was never questioned in the case, even though friends reportedly told police they were suspicious when he didn’t show up for Mess’s memorial service.

In May 2013, Ibragim Todashev, a boxer who was also friends with Tamerlan Tsarnaev, was shot and killed by an FBI agent who was interviewing him about the case. According to a filing by federal prosecutors last fall, Todashev had implicated himself and Tamerlan Tsarnaev in the murders before he was killed.

As recently as this spring, the investigation into the Waltham slayings appeared to be ongoing. In April, a federal grand jury looking into the murders subpoenaed Katherine Russell, Tamerlan Tsarnaev’s widow, for items that belonged to Mess. But her attorney, Amato DeLuca, said she didn’t have anything.

Story continues

The Waltham case has been the subject of a back and forth between federal prosecutors and Dzhokhar Tsarnaev’s defense team, who have repeatedly pressed the government for months to share its evidence and information about the murders. Prosecutors have pushed back, insisting the Waltham case isn’t relevant because Tamerlan Tsarnaev is not on trial.

But Dzhokhar Tsarnaev’s attorneys, who appear to be crafting a defense based around casting the older brother as a bullying mastermind of the Boston operation, renewed their push for evidence on Friday, arguing the government had previously said the case was “might be relevant if Dzhokhar were aware of it.” They then pointed to a letter they received from prosecutors on Aug. 15, 2014, saying the government had a witness prepared to testify that “Dzhokhar had such an awareness.”

The developments come just days before both sides are scheduled to release their initial list of witnesses in the bombings trial, which is scheduled to begin in January. Both sides are due in a Boston courtroom on Oct. 20 for status hearing in the case. Prosecutors have asked that Tsarnaev, who has not been seen in court since July 2013, when he was formally charged in the attacks, make an appearance, but it’s unclear if he will.

Tsarnaev has pleaded not guilty in the bombings. If convicted, he faces the death penalty.