A source said that the FBI had been investigating Todashev for about a month.
The FBI had followed Todashev for days, his friend told CNN affiliate Central Florida News 13.
Todashev "wasn't like real close friends (with Tsarnaev), but he just happened to know him," Khasuen Taramov told the TV station. "But he had no idea that they were up to something like that, like bombings and everything, you know what I mean?"
He told CNN affiliate WESH that Todashev and Tsarnaev had spoken by telephone about a month before the bombings.
"It was a complete shock to him," Taramov said.
The two met a couple years ago in Boston, where Todashev had lived and where there is a small, close-knit community of Chechens, said Taramov.
Their telephone conversation before the bombings contained nothing but routine pleasantries, he said. "It was 'How are you doing; how's your family?' That's all."
Taramov said he himself was questioned by the FBI for three hours Tuesday night. Asked what he was asked, Taramov said, "Different kind of questions like 'what do you think about bombings,' 'do you know these guys,' blah blah blah, what is my views on certain stuff."
He said Todashev was not a radical. "He was just a Muslim. That was his mistake, I guess."
Taramov said his friend had told him he had a bad feeling about the direction the investigation was heading.
"He felt like there's going to be a setup ... bad setup against him. Because he told me, 'They are making up such crazy stuff, I don't know ... why they doing it. OK, I'm answering the questions, but they are still making up some, like, connections, some crazy stuff. I don't know why they are doing it.' "
Before meeting with the FBI for a 7:30 p.m. interview Tuesday, Taramov said, his friend asked him to take his parents' telephone numbers. "He just told me, 'Take the numbers, in case something happens, if I get locked up, or whatever, call them.' You know what I mean?
"We were expecting to get him locked up, but not getting him killed. I can't believe it."
Todashev was unemployed and had been living on insurance money he received after surgery for an accident. "He used to be a fighter, MMA fighter," Taramov said, in a reference to mixed martial arts.
Todashev was arrested this month on a charge of aggravated battery after getting into a fight over a parking spot with a man and his son outside an Orlando mall. The son was taken to a hospital with head injuries, a split upper lip and several teeth knocked out of place, the Orange County Sheriff's Office said in a report.
"Todashev said he was only fighting to protect his knee because he had surgery in March," the report said. He told the police that he was a former mixed martial arts fighter, it said.
Todashev, described as 5-foot-9 and 160 pounds, was released on $3,500 bond.
Asked about the incident, Taramov downplayed it. "He had a fight in the parking lot, the two guys jumped on him ... pretty much he just defended himself against two," he told WESH. "The only mistake: he did kick their ass and left."
Todashev had recently gotten his green card and had been planning to visit his parents in Chechnya and then return to the United States, but canceled the plans, Taramov said.
Now, he added, he was planning to call his friend's parents.