Ibragim Todashev, who was killed during an FBI interview last week, was unarmed when he was fatally shot, fueling speculation that his association with Boston Marathon bombing suspect Tamerlan Tsarnaev was enough, in the eyes of police, to be fatal.

The death of Ibragim Todashev has been shrouded in mystery since he was mortally wounded during an interview with FBI agents on May 22. Before Wednesday's admission that the 27-year-old was unarmed at the time of his death, investigators offered conflicting accounts of what happened in Todashev's final minutes.

Todashev associated with Tamerlan Tsarnaev from mixed martial arts and boxing circles in the Boston area before he moved from Cambridge, Massachusetts to Orlando, Florida. FBI officials maintained he was never a suspect in the Boston Marathon bombing.

Investigators did say, however, that the matter would be the subject of a probe that is expected to last for several months.

"The FBI takes very seriously any shooting incidents involving our agents and as such we have an effective, time-tested process for addressing them internally," FBI spokesman Paul Bresson said in a statement Wednesday.

"The review process is thorough and objective and conducted as expeditiously as possible under the circumstances."

One federal agent, according to the Washington Post, claimed Todashev was shot after trying to grab an agent's sidearm. A second agent claimed Todashev brandished a knife. A Bureau statement issued on the day of the incident said only that an "individual" being interviewed was killed when a "violent confrontation was initiated by the individual."

Law enforcement officials speaking anonymously said Todashev did implicate himself and Tsarnaev in connection with a triple murder in Waltham, Massachusetts on September 11, 2011. On September 12 police found three dead men in a well-kept rental home. Their throats had reportedly been slashed and bodies covered in marijuana.

The spokeswoman for Middlesex County's district attorney's office only told the Post that the investigation was ongoing, refusing to speculate as to whether Todashev or Tsarnaev were suspects. Sources close to the investigation said Todashev was friends with one of the victims.