At some point before he was shot to death in a confrontation with the FBI, Ibragim Todashev tied his buddy Tamerlan Tsarnaev’s to a triple murder in Waltham, according to papers filed in U.S. District Court in Boston.

“According to Todashev, Tamerlan Tsarnaev participated in the Waltham triple homicide,” reads a motion filed by federal prosecutors.

Prosecutors are trying to stop defense lawyers for Dzhokhar Tsarnaev from obtaining documents related to the elder Tsarnaev’s purported role in the Waltham slayings. In the filing, they state it could hurt the investigation into the Sept. 11, 2011 crime by the Middlesex District Attorney’s office.

“Disclosure of the details of that investigation could jeopardize it. (Dzhokhar) Tsarnaev, in contrast, has no urgent need for the privileged investigative materials he seeks. Even assuming, as Tsarnaev claims, that ‘the nature and extent of Tamerlan’s alleged involvement’ in the Waltham triple homicide is ‘critical mitigation information,’ … this case has not yet even been set down for a trial date, let alone sentencing,” prosecutors state.

The Middlesex District Attorney’s office did not responded to a request for comment tonight.

The elder Tsarnaev was killed during a shootout with cops in Watertown April 19. His brother was captured later and faces the death penalty for his alleged role in the April 15 marathon bombings.

All three victims in Waltham were stabbed in the neck in exactly the same manner, the medical examiner said. The victims were identified as Brandon Mess, 25, of Waltham; Erik Weissman, 31, of Cambridge; and Raphael Teken, 37, of Cambridge.