Ibragim Todashev was fatally shot early Wednesday during an interview with the FBI and Massachusetts State Police in Orlando, Florida, CNN reported citing a federal law enforcement official.
But before he was shot, Todashev not only confessed to his direct role in slashing the throats of three people in Waltham, Massachusetts, but also fingered Tsarnaev in the deaths, the official said.
Todashev was being questioned about the slayings and his acquaintance with Tsarnaev, when he attacked an FBI agent, who shot him dead, CNN said.
The unsolved triple murder received renewed interest after it was learned that Tsarnaev had been a good friend of one of the Waltham victims.
According to the channel, Todashev told investigators the men were killed during a drug ripoff because he and Tsarnaev were afraid they would be able to identify them and tell police what happened.
So far, no link has been found between Todashev and the Boston Marathon bombings. However, the FBI is looking into the many connections between Todashev and Tsarnaev, whose radicalisation allegedly led to the Boston bombings.
CNN citing a federal law enforcement official said they were initially led to Todashev because they learned he knew Tsarnaev and his younger brother, Dzhokhar. They also said cell phone records connected Tamerlan and Todashev.
Todashev was being interviewed in the kitchen of his Florida home. He grabbed a knife, which is why fatal force was used, the channel said citing a source.
Investigators are awaiting test results to determine whether Todashev's DNA was found at the Massachusetts triple murder scene and whether the DNA of Tamerlan Tsarnaev also was found there.
Todashev and Tsarnaev were were members of the mixed martial arts forum Sherdog.com, along with Russian-Canadian boxer-turned-jihadist William Plotnikov, CNN reported citing a source.