The bribery case of an Illinois lawmaker may take a rare step this week. Attorneys are scheduled to debate whether federal authorities lied about the background of a key witness who secretly recorded Illinois State Rep. Derrick Smith.

Prosecutors allege they have Smith on tape saying he wants a $7,000 bribe in cash so there would be no trace of the money. Much of the prosecutors’ initial complaint relies on secretly recorded conversations Smith had with an unnamed source.

Now, that anonymous source has become the subject of scrutiny.

Victor Henderson, Smith’s defense attorney, said federal authorities didn’t disclose the criminal history of that source. Early on in the case, federal investigators said the source had one prior arrest and had been paid $1,200 by the FBI for work in other cases.

But both prosecutors and the defense now say that was wrong. The source actually had 20 prior arrests and had been paid $2,100 by the FBI.

“It makes a big difference when you’re starting a case out whether you have a nun or a Sister Bertrille who’s at the center of it, or a confidential informant who’s got a criminal history that’s 40 pages long,” Henderson said.

Henderson is calling for the anonymous source and federal agents to testify in a hearing into whether the evidence could be used in Smith’s trial, which is scheduled to begin in October.

Meantime, prosecutors argue in court documents the hearing isn’t necessary because the witness’s background doesn’t change what Smith said on tape.

Since the charges were brought against Smith, his fellow members of the House of Representatives voted to kick him out of office. But voters in Smith’s district on Chicago’s west and northwest side voted him back into his old seat in November after a contentious election. At one point during the campaign, the politically powerful Secretary of State Jesse White, who had once supported Smith, told a crowd of ministers that Smith was no longer welcome on the West Side of Chicago.

“Someone told me that when you take money, make sure you take enough so you can afford a lawyer,” White said, mocking the $7,000 Smith is accused of illegally accepting.

Shortly after Smith won election, Henderson held a news conference in which he told reporters Smith would be an independent voice in Springfield who would stand up to the legislators who expelled him from public office.

“There were a lot of ministers who didn’t want Martin Luther King up here in the ’60s because he said he was causing problems. Look what good he did. People wanted Nelson Mandela to be quiet. People wanted Jesus to be quiet,” Henderson said in November.

Lawmakers in Springfield have abandoned attempts to kick Smith out of office again since the state constitution forbids a legislator from being expelled twice for the same reason. Republican State Rep. Jim Durkin, who helped expel Smith last year, has said Smith will have a hard time doing his job since so many House found him unfit to hold public office once before.

“He will have a very difficult time legislating and, quite frankly, I think that members of the legislature are going to be suspicious of him and some of them will be just downright offended that they’re serving with him,” Durkin said.