Dead Boston bombing suspect Tamerlan Tsarnaev and another man — who was killed by the FBI on Wednesday — murdered three people in Massachusetts after a drug deal went wrong in 2011, law enforcement sources tell NBC News.

Sources say that what began as a drug ripoff ended in a triple homicide when Tsarnaev and friend Ibragim Todashev realized their victims would later be able to identify them.

Todashev was killed by a federal agent while giving a statement on his role on Wednesday in Orlando, Fla.

The man who was shot, Todashev, 27, allegedly attacked an agent with a knife while confessing to the 3-year-old slayings. He was not suspected of having played any role in the bombing that killed three people and injured scores more in April, but he did confess to being involved in a brutal Boston-area slaying two years ago, investigators said.