Prosecutors said in a court filing Friday they don't have any new evidence that the brother of Boston Marathon bombing suspect Dzhokhar Tsarnaev was involved in a 2011 triple slaying and have no witness who will testify to what Tsarnaev knew about his brother and the killings.
The government made the statements in response to Tsarnaev's lawyers' request earlier this month for information about a witness they said the government previously mentioned.
Defense lawyers are seeking information that could show Tsarnaev was influenced by his brother in the 2013 bombings.
Prosecutors said Friday they had disclosed only that a third party told investigators there was someone who might say Tsarnaev knew his brother Tamerlan was involved in the so-called Waltham killings.
"Whether that person would actually say it, let alone testify to it, is another matter entirely," prosecutors said. "The government has no evidence that Tamerlan Tsarnaev actually participated in the Waltham murders, so there is nothing to produce."
The government also repeated its argument that the facts of the 2011 case and what someone says Tsarnaev knew about it are irrelevant to Tsarnaev's state of mind when the bombings took place.
Dzhokhar Tsarnaev has pleaded not guilty to 30 federal charges and could face the death penalty if convicted at his trial, scheduled to begin in January.
Prosecutors say the Tsarnaev brothers planted two pressure-cooker bombs near the finish line of the April 15, 2013, marathon, killing three people and injuring more than 260. Tamerlan died following a shootout with police three days after the bombings.
In court papers a year ago, federal prosecutors said a friend of Tamerlan Tsarnaev told investigators Tamerlan participated in the unsolved killings of three men found in Waltham with their throats slit and sprinkled with marijuana. The friend, Ibragim Todashev, was shot to death by authorities while being questioned in Florida last year.
Prosecutors said a judge has already ruled they didn't have to give the defense a written or recorded account of Todashev's statement, and there's no reason to reconsider. Prosecutors also said the Middlesex district attorney has told them the Waltham investigation "remains active and ongoing."
In a separate filing Friday, Tsarnaev's lawyers complained for a third time about media leaks they say are jeopardizing his right to a fair trial.
They cited a recent Newsweek magazine piece containing statements from unnamed law enforcement sources. They say the article "casts the entire Tsarnaev family in an extremely negative light" and "suggests that others were somehow involved."
Tsarnaev's lawyers want U.S. District Judge George O'Toole Jr. to hold a hearing and call supervising law enforcement officers to testify about their efforts to stop unauthorized communications with the news media.
O'Toole has rejected two earlier defense requests for a hearing, but has told prosecutors to warn law enforcement against disclosing information about the case to the media. Prosecutors sent a letter about the judge's concerns to law enforcement agencies involved.
Also Friday, Tsarnaev's lawyers said in a filing that they do not believe they are required to file a list of defense witnesses before Tsarnaev's trial. They said they are worried that once the defense witness names are turned over to prosecutors, the witnesses would decide not to testify, "given the virtual certainty that the FBI will descend on each of the non-expert witnesses to interview them."
His lawyers said they have encountered "unusual and severe obstacles" in trying to get witnesses who knew Tsarnaev and his family to testify.
A spokeswoman for prosecutors declined to comment.