Prosecutors from Florida and the U.S. Justice Department have concluded that an FBI agent did not violate any laws when he shot and killed a man he was questioning about last year's bombings at the Boston Marathon, according to officials familiar with their findings.

Ibragim Todashev, a 27-year-old Chechen man, was killed last May at his home in central Florida. The FBI and state police from Massachusetts were there to ask him about his friendship with Tamerlan Tsarnaev, the older of the two brothers accused in the bomb attacks who was killed in a shootout with police four days after the bombings.

The FBI said at the time that an agent fired his gun when Todashev, a former mixed martial arts competitor, lunged at him with a weapon. Massachusetts investigators were also questioning him about the murder of three people in Waltham, Mass., in 2011. The victims were found in an apartment with their throats slit and their bodies sprinkled with marijuana. Friends of the three men have said that one of them knew Tamerlan Tsarnaev.

Last year, federal prosecutors disclosed in court filings that Todashev told the FBI agent in May that "Tamerlan Tsarnaev participated in the Waltham triple homicide."

The shooting was investigated by Jeff Ashton, the Florida state's attorney for Orange and Osceola counties. His findings are to be formally announced next week.

Tsarnaev's younger brother, Dzhokhar, awaits trial for the marathon bombings. He has pleaded not guilty. The Justice Department has notified his lawyers that it intends to seek the death penalty if he is convicted. No trial date has been set.

— Pete Williams