Accused terrorist Dzhokhar Tsarnaev allegedly knew his older brother, Boston Marathon bombing accomplice Tamerlan Tsarnaev, was involved in the 2011 killing of three Massachusetts men, reports UPI.

“The government disclosed that an identified witness would be prepared to testify” that Dzhokhar had knowledge of the involvement of his brother in the grisly slayings, according to a motion the defense team for Tsarnaev filed in the U.S. District Court on Friday.

Attorneys for the younger Tsarnaev, who was 19 years old at the time of the bombing, intend to argue Tamerlan was the dominant perpetrator. The defense attorneys filed the motion to gain access to documents related to the 2011 case. The evidence could be vital in demonstrating the relative culpability of the two brothers, argue the defense attorneys.

Tamerlan was 26 years old when he was killed in a shootout with cops on April 18, 2013, three days after the Boston Marathon bombing that killed three people and injured 260 others. A friend of Tamerlan reportedly implicated him in the triple homicide only moments before his death.

“Information and evidence tending to show that Tamerlan Tsarnaev participated in a triple homicide in 2011, and information depicting the brutality of those murders, is critical to the defense team,” read the motion.

If the evidence is proven credible, it could close a triple homicide case that went quickly cold. On September 12, 2011, three local men–Brandon Mess, 25, Erik Weissman, 31, and Raphael Teken, 37–were found with their necks slit, and marijuana sprinkled over their bodies in a Waltham, Massachusetts apartment.

Tamerlan Tsarnaev had been a frequent visitor to the apartment, said the girlfriend of Mr. Mess to police soon after the slayings. She was the first to assert that police investigating the killings knew Tsarnaev, who had been questioned in 2011 by the FBI for possible terrorist connections, had ties to the three victims.

At the time, investigators assumed the killings were drug-related.