Last Updated Mar 25, 2014 1:00 PM EDT
State Attorney Jeff Ashton said in a report the agent was "justified in self-defense" in shooting Ibragim Todashev, 27, last May. The officers were questioning Todashev about the 2011 slaying in Waltham, Mass., and he was about to write a statement when his mood changed from cooperative to agitated, according to the report.
Todashev, a mixed martial arts fighter, flipped a coffee table in the air, knocking down the FBI agent and causing a bloody gash on the agent's head. Todashev then ran past the two officers, into the kitchen and returned with a pole - a long metal handle of a broom or mop - that he pointed at the Massachusetts officer, the report said.
The FBI agent fired three or four shots at Todashev as he charged toward the trooper, and Todashev dropped to his knees. But he still managed to lung at the officer, and the FBI agent fired three or four more shots, the report said.
"The one common thread among all was the observation that he was, at his core, a fearless fighter," Ashton said in a letter to FBI Director James Comey. "Perhaps on this occasion, he simply reverted to that basic aspect of his personality and chose to go down fighting."
Separately, the U.S. Justice Department also concluded Tuesday that there was no basis for federal criminal charges against the FBI agent. The federal inquiry echoed the Florida report in saying that Todashev implicated himself in the triple-murder.
Federal authorities have said in court filings that Todashev also implicated Tamerlan Tsarnaev in the Waltham slayings, but the Justice Department report said the details of the confession were not being released publicly at the request of prosecutors in Massachusetts. The Justice Department report said both men shared an interest in mixed martial arts and were suspected in the Waltham murders.
In the Waltham case, three men were found in an apartment with their necks slit and their bodies reportedly covered with marijuana. One of the victims was a boxer and friend of Tsarnaev, who had befriended Todashev when Todashev lived in Boston.
In the Florida shooting, the FBI agent from Boston and two Massachusetts State Police officers had questioned Todashev at his apartment for almost five hours before the fatal shooting, the report said. The FBI had become interested in Todashev in the days after the Boston marathon bombing last April because he was friends with Tsarnaev. By then, Todashev also had become a "person of interest" in the Waltham slayings, according to the report, and FBI agents had questioned him several times in the weeks before he was killed.
One of the Massachusetts troopers told investigators that Todashev's mood changed right before he was to sign the statement.
Todashev asked to go to the bathroom and then asked for more cigarettes even though he seemed to have plenty in his pack, raising worries that he was trying to minimize the number of law enforcement officers in room, the trooper told investigators. On the trip back from bathroom, the trooper became more concerned as they walked downstairs because Todashev appeared to be purposely walking slowly. As a precaution, the trooper grabbed a samurai sword hanging on a wall and hid it in the kitchen.
"I was more and more concerned he might try to flee or attack us," the trooper told investigators.
The trooper also sent a text message to the FBI agent and the second trooper: "Be on guard, he is in a vulnerable position to do something bad. Be on guard now. I see him looking around at times."
After Todashev waived his Miranda rights and started writing a statement, one of the troopers stepped outside to call a prosecutor in Massachusetts. Todashev flipped the table, and he "moved incredibly quickly, almost like something in a movie," the trooper in the room told investigators. Todashev grabbed the pole, stood in a fighting position and "charged toward me as if he was going to impale me with the pole," the trooper said.
The FBI agent told investigators, "There was no doubt in my mind that Todashev intended to kill us both."
An autopsy report also released Tuesday showed Todashev was shot once in the head and six times in the torso.
Todashev's family has raised doubts about the account provided by law enforcement, saying that Todashev was recovering from knee surgery and was limping at the time he was killed.
Last week, Todashev's widow spoke to CBS station WBZ-TV exclusively by phone from Russia.
"No. I don't believe it," Reni Manukyan said of the initial reports of the investigation. "Besides that, there were so many different versions of what happened. They had released so many different things that he was with a gun, with a knife, with a grate, with a broomstick, with a chair."
Todashev's father, Abdul-Baki Todashev, insisted last year that his son was unarmed and said that U.S. agents killed his son "execution-style." At a May news conference in Moscow, Abdul-Baki Todashev showed journalists 16 photographs that he said were of his son, Ibragim, in a Florida morgue. He said his son had six gunshot wounds to his torso and one to the back of his head and the pictures were taken by his son's friend, Khusen Taramov.
Hassan Shibly, executive director of the Council on American-Islamic Relations in Tampa, which is conducting its own investigation into the fatal shooting, said Ashton's investigative focus was very narrow.
"It's very important that this isn't whether the agent was justified in shooting," Shibly said. "It's about the pattern of abuse that occurred before, during and after the questioning. That won't be covered in a criminal investigation."
Last year, former CBS News senior correspondent John Miller discussed the questions regarding reasonable use of force in the standoff that led to Todashev's death.
"I was trained in the FBI policy on use of force," Miller said. "The standard is if you believe you or your partner or somebody with you is going to be the victim of either serious bodily harm or possibly death, you have the right to use deadly physical force."
Authorities allege that Dzhokhar Tsarnaev, 20, and 26-year-old Tamerlan Tsarnaev, ethnic Chechens from Russia, planned and carried out the twin bombings near the finish of the marathon on April 15. Three people were killed and more than 260 were injured.
Dzhokhar Tsarnaev faces 30 federal charges, including using a weapon of mass destruction and 16 other charges that carry the possibility of the death penalty.
Tamerlan Tsarnaev died in a gunbattle with police as authorities closed in on the brothers several days after the bombings.