The FBI says one of its agents shot dead a man being questioned over links to one of the Boston marathon bomb suspects because he turned violent.

The shooting happened at an apartment complex in Florida.

Ibragim Todashev was being interviewed about links to Tamerlan Tsarnaev.

Todashev was of Chechen origin like the Tsarnaev brothers who are suspected of carrying out the bombings.

A friend of Todashev said he knew Tsarnaev but wasn't involved in the attack and had wanted to leave the country.

(SOUNDBITE)(English) KHUSN TARAMIV, FRIEND OF IBRAGIM TODASHEV, SAYING:

"He cancelled the tickets because the FBI had been like, I don't know, they'd been pushing him, you know what I'm saying, they'd been pushing him. They said 'don't leave, don't leave' so he decided to stay. But we had a feeling, worst case scenario, that something like that's going to happen, you know what I mean? And it happened eventually and we tried to avoid it."

Three people were