The man we're talking about is Richard Aoki -- a Japanese American who was a leader in the predominantly African American Black Panther party. He was known as a militant and a radical activist against the establishment -- the very same establishment that it turns out he was secretly working for as an informant to the FBI.
Whether storming the state Capitol or walking the streets of Oakland, the Black Panthers were known for openly carrying firearms. Army veteran Richard Aoki was known as the left-wing activist who supplied some of their guns and taught them how to shoot. But there was a side of him that even his closest allies didn't know about.
"Him even talking to the FBI, yeah, so that's kind of a shocking thing for me to hear," friend Harvey Dong said.
Aoki wasn't just talking to the FBI but regularly informing on the Black Panther party's activities. It came to light in recently obtained FBI documents listing some of the bureau's confidential sources.
"Most of their names were blacked out, but for some reason, Richard Aoki's name had not been blacked out and he was listed in the report as informant T-2," Rosenfeld said.
Rosenfeld says a former FBI agent he interviewed for his new book immediately recognized Aoki's name.
"And he says, 'Aoki was my informant; I developed him,'" Rosenfeld said.
The agent said he asked Aoki to start going to meetings of left-wing groups and to report back on what he heard. As he worked his way into a leadership role, Aoki became one of the bureau's best sources.
Retired agent Wes Swearingen says being Japanese may have helped him keep his cover. "Nobody's going to guess that he might be an informant," he said. "In San Francisco, he can meet with a Japanese FBI agent out in the public. They can have lunch."
But while Aoki gave the FBI valuable information, he was also putting guns in the hands of radicals.
"He provided not only weapons but weapons training," Swearingen said. "The question I had was, did the FBI know that Richard Aoki was arming the Black Panthers?"
Swearingen says the answer is likely in Aoki's main file -- a file the FBI still hasn't made public.
"They definitely would've had that information placed somewhere," Swearingen said.
Three years ago, Aoki committed suicide after a long battle with illness. At the time, his connection to the FBI was still a secret, but his patriotism was not. Authorities found his body next to two neatly-pressed uniforms -- one from the Black Panthers, the other from the Army.
Rosenfeld's book "Subversives: The FBI's War on Student Radicals, and Reagan's Rise to Power" was published by Farrar, Straus and Giroux.