Three law enforcement officials, speaking on condition of anonymity, said Todashev had lunged at the FBI agent with a knife. However, two of those officials said later in the day it was no longer clear what happened. The third official had not received any new information.
The FBI gave no details on why it was interested in Todashev except to say that he was being questioned as part of the Boston investigation.
But some of his former roommates who were questioned as well said that Todashev knew one of the bombing suspects, Tamerlan Tsarnaev, from mixed martial arts fighting in Boston and that the FBI was asking about him.
Public records show Todashev lived in Watertown, Mass., just outside Boston, last year.
Tamerlan Tsarnaev, an aspiring boxer, was killed in a shootout with police days after the April 15 bombings. His younger brother, Dzhokhar, survived and is charged with carrying out the attack that killed three people and wounded more than 260.
Investigators have been trying to establish the scope of the plot. In addition, authorities in Massachusetts said they would investigate whether Tamerlan Tsarnaev had any connection to an unsolved 2011 slaying in the Boston suburb of Waltham, where three men were found dead in an apartment, their throats slit and marijuana sprinkled over their bodies. One of the victims was a boxer and a friend of Tsarnaev's.
Todashev had lived on and off with other Chechens in the Orlando suburb of Kissimmee and had moved to Orlando more recently, friends said.
"He's a regular guy, nothing wrong," Saeed Dunkaev said.
Police records, however, suggest he had a hot temper, with arrests in a road-rage incident and, more recently, in a fight over a parking space.
Muslin Chapkhanov, another former roommate, said Todashev knew the older Tsarnaev brother. Todashev "was living in Boston and I think he trained with him," Chapkhanov said.
Former roommate Khusen Taramov said the FBI was asking questions about a conversation Todashev had with the elder bombing suspect a month before the Boston attack.
The Tsarnaev brothers have roots in the turbulent Russian regions of Dagestan and Chechnya, which have become recruiting grounds for Islamic extremists. Investigators have said the brothers carried out the bombing in retaliation for the U.S. wars in Muslim Iraq and Afghanistan.
An FBI team was dispatched from Washington to review the shooting, standard procedure in such cases.
Todashev was arrested earlier this month on a charge of aggravated battery after getting into a fight over a parking spot with two men — a father and son — at an Orlando shopping mall. The son was hospitalized with a split lip and several teeth knocked out, according to a sheriff's report. Todashev claimed self-defense.
"Also by his own admission Todashev was recently a former mixed martial arts fighter," the arresting deputy said in his report. "This skill puts his fighting ability way above that of a normal person."
Todashev was released on $3,500 bail after his May 4 arrest. His attorney, Alain Rivas, didn't immediately respond to a call for comment Wednesday.
Todashev was also arrested by Boston police in 2010 after a road-rage incident. Witnesses told police that he argued with two other drivers and cut them off with his vehicle. He yelled, "You say something about my mother, I will kill you," according to a police report.