The FBI says a man being questioned in the Boston Marathon bombings probe was fatally shot when he initiated a violent confrontation.
The FBI identified the man as Ibragim Todashev.
The shooting incident took place on May 22 in Orlando, Florida, where an FBI agent along with other law-enforcement personnel were questioning him.
The FBI agent was taken to hospital with injuries that were not life-threatening.
In a statement, FBI spokesman Paul Bresson said the FBI agent acted on an "imminent threat" and shot Todashev.
The FBI gave no details on what investigators had hoped to learn from Todashev.
U.S. media reports said 27-year-old Todashev was an ethnic Chechen who had ties with Tamerlan Tsarnaev, one of the suspects in the Boston Marathon bombings.
The April 15 bombings killed three people and wounded more than 260.
Tamerlan Tsarnaev, 26, was killed following a shoot-out with police four days after the bombing.
His brother, 19-year-old Dzhokhar Tsarnaev, was captured after a manhunt later that day.
He could face the death penalty, if convicted.
The Tsarnaev brothers were ethnic Chechens with roots in Russia's volatile North Caucasus region.
A man who described himself as a friend of Todashev told local television stations that Todashev knew Tamerlan Tsarnaev through their shared hobby of mixed martial-arts fighting.
He said law-enforcement agents began questioning and following Todashev soon after the Boston bombings.
Police in Florida said Todashev had been arrested on May 4 and charged with aggravated battery with great bodily harm.
The Associated Press said Todashev was arrested after a dispute over a parking spot at an Orlando shopping center.
The report said he was later released on bail.
With reporting by AP, Reuters, and the BBC