Turner is standing by his decision

“I’m a public official,’’ the goateed, 70-year-old politician told reporters after testimony concluded for the day. “I’ve taken an oath to serve the public. I have to testify. I say I’m innocent. Why should I be afraid of going before anybody?’’

Legal specialists say Turner’s plan to testify, possibly as early as today, could prove perilous by shifting the focus of the trial from the government’s evidence against him to the credibility of the six-term councilor. But Turner, who conceded before trial that his lawyers advised him not to take the stand, said attorneys operate in a different realm.

“I’ve been accused of a horrible crime for a public official,’’ said Turner, a longtime community activist accused of taking a $1,000 bribe on Aug. 3, 2007, from a witness secretly cooperating with the FBI. “I have to take that witness stand, even though it might result in my going to jail. . . . Something is dreadfully wrong if you don’t expect me to take the witness stand. You should be saying, ‘Right on, Chuck, that’s what we expect you to do.’ ’’

At that, a supporter flanking Turner outside the federal courtroom yelled, “Right on, Chuck!’’

The government is expected to rest today or tomorrow, giving the defense a chance to call Turner.

Earlier yesterday, Boston businessman Ronald Wilburn, the cooperating witness who broke with the government and testified only after a judge threatened to jail him, left the courtroom after his third and final day on the stand. He told reporters in the corridor that Turner will be convicted of lying to the FBI.

“They’re going to kill him on perjury,’’ Wilburn said, referring to the US District Court jury. “He killed himself on perjury at least four times. He’s gone.’’

Turner is on trial on charges of attempted extortion and on three counts of lying to federal agents who interviewed him 14 months after he allegedly accepted the cash in exchange for helping Wilburn secure a liquor license. Wilburn secretly videotaped and audiotaped the purported payoff in Turner’s district office in Roxbury.

During an interview by FBI agents on Oct. 28, 2008, at City Hall, Turner allegedly lied about having accepted the $1,000, about Wilburn offering to hold a fund-raiser for him and about Wilburn offering to give him money or other help.

The jury is “going to crucify’’ him on those charges, Wilburn said.

Turner, he added, was an afterthought in the FBI sting that captured state Senator Dianne Wilkerson accepting $23,500 in bribes from Wilburn and undercover FBI agents in 2007 and 2008. She pleaded guilty to attempted extortion charges on June 3 and awaits sentencing.

“He wasn’t even on the radar screen,’’ the dapper, 71-year-old witness said.

On the stand yesterday, Wilburn repeated that he handed to Turner the $1,000 that an FBI agent had given him. Under questioning by Assistant US Attorney John T. McNeil, Wilburn also appeared to startle prosecutors by offering an unsolicited demonstration of how he passed the money.

Using props that he had brought to the witness stand at his own initiative, Wilburn held up what resembled a roll of bills secured with a rubber band. He could have passed the cash this way, he said, gesturing, but did not. Raising a stack of index cards, he said he plucked the cash out of his pocket with his left hand while the bills were flat, passed them to his right hand, and gave them to Turner while shaking hands.

“I had the money flat out on my hand’’ at one point, he said.

The videotape of the alleged payoff did not reflect that. When the tape was played normally last week, it was impossible to see money changing hands at all. But when it was slowed down and clicked frame by frame Thursday, Wilburn pointed to something green in his hand, and it appeared to be a lump.

In other testimony under questioning by McNeil, Wilburn said that when he signed an employment agreement with the FBI in May 2007 to work as a cooperating witness, his wife was earning nearly $70,000 a year at Fidelity Investments, and his adult daughter, who lived with the couple, earned about $55,000 at PetSmart. The testimony was apparently intended to undercut the defense suggestion that Wilburn cooperated with the FBI, earning $29,099, because he needed money.

Under cross-examination by Turner’s lawyer, Barry P. Wilson, Wilburn acknowledged that his wife lost her job in 2008 and that his only personal income in addition to what he received from the FBI was from Social Security and a modest annuity.

Saltzman can be reached at jsaltzman@globe.com.