Dzhokhar Tsarnaev’s friend offered to testify Tsarnaev knew his brother was involved in Waltham triple slaying

Boston Marathon bomber Dzhokhar Tsarnaev (right) posed with Azamat Tazhayakov (left) and Dias Kadyrbayev in New York. Immigration officials say Kadyrbayev has been deported to his native Kazakhstan after he was convicted of concealing evidence in the case.REUTERS

Newly unsealed court documents in the case against Boston Marathon bomber Dzhokhar Tsarnaev provide new insight — and raise new questions — about a still-unsolved 2011 triple murder in Waltham.

One document revealed that Tsarnaev’s college classmate Dias Kadyrbayev was the previously unnamed prosecution witness offering to testify that Tsarnaev knew that his older brother was involved in the Waltham killings.

Kadyrbayev said Dzhokhar Tsarnaev told him in the fall of 2012 that Tamerlan “had committed jihad” in Waltham, according to an August 2014 letter from federal prosecutors describing conversations they had with Kadyrbayev’s attorney just days before Kadyrbayev pleaded to conspiracy and obstruction charges.

On Sept. 12, 2011, Brendan Mess, 25, once a close friend of Tamerlan’s, Erik H. Weissman, 31, and Raphael M. Teken, 37, were discovered in Mess’s apartment with their throats slit and marijuana scattered on their bodies. Presumed to be a drug-related crime, the case went cold.

Nearly two years later, Tsarnaev and his younger brother, Dzhokhar, planted two bombs near the Marathon finish line that killed three people and wounded more than 260 others in April 2013. The brothers also killed an MIT police officer.

Tamerlan Tsarnaev was killed in a police shootout in Watertown a few days after the bombing, and his brother has been convicted and sentenced to death in the bombing. The documents were unsealed as Dzhokhar Tsarnaev pursues an appeal of his sentence.

Kadyrbayev, Dzhokhar Tsarnaev’s friend at the University of Massachusetts Dartmouth, pleaded guilty to trying to throw away Dzhokhar Tsarnaev’s laptop and a backpack containing explosive powder from fireworks after he recognized Tsarnaev in FBI photos released to the public after the bombings.

Kadyrbayev was released from federal prison in August and was due to be deported to Kazakhstan, where he is a citizen.

The Middlesex district attorney’s office, which has been investigating the Waltham killings, has remained tight-lipped about the case. No one has been charged.

A month after the Marathon bombing, Tamerlan Tsarnaev’s friend, Ibragim Todashev, 27, was fatally shot after attacking an FBI agent and State Police officer in Florida. He had allegedly confessed on tape to helping Tamerlan kill the three men in Waltham.

Dzhokhar Tsarnaev’s attorneys sought unsuccessfully during the trial to raise the Waltham case to paint a picture of Tamerlan Tsarnaev as the mastermind behind the bombings and Dzhokhar Tsarnaev as a pawn acting under his older brother’s influence.

Another unsealed document showed that online searches for information about the Waltham killings were made about one week after they happened on a laptop computer belonging to Tamerlan Tsarnaev’s wife, Katherine Russell.

On Sept. 18, 2011, a search was made for “3 men killed in waltham.” The following day, another search was made for “men killed in waltham” and then just three minutes later a search for “tamerlan tsarnaev,” according to a filing by Dzhokhar Tsarnaev’s attorneys.

Dzhokhar Tsarnaev’s attorneys said it wasn’t clear who conducted the searches, nor did they know what, if any, computer Tamerlan Tsarnaev was principally using in September 2011.

But they said the searches provided “additional circumstantial evidence of a connection” between Tamerlan Tsarnaev and the killings.

Yet another unsealed document raised new questions about Khairullozhon Matanov, a Quincy cab driver who was a friend of the Tsarnaev brothers and who took them both out to dinner only hours after the bombings.

In a previously sealed transcript of discussions in the spring of 2015 among prosecutors, defense attorneys, and the judge in Dzhokhar Tsarnaev’s case, the defense mentioned an FBI summary of an interview with Matanov in which agents questioned him about money wired to Russia sometime after the Waltham killings.

Miriam Conrad, one of Dzhokhar Tsarnaev’s attorneys, said Matanov was “apparently” roommates with Todashev at the time of the Waltham killings, according to the testimony.

In June 2015, Matanov was sentenced to serve 30 months in prison followed by three years of supervised release and faced deportation to his native Kyrgyzstan after agreeing to plead guilty to charges that he lied to investigators about the times he saw and communicated with the Tsarnaevs after the bombings.

Matanov also acknowledged that he deleted pro-jihadi documents from his computer after he recognized the Tsarnaevs as the suspected bombers, after their photos were released by the FBI.