Philadelphia District Attorney Seth Williams has accepted a demand that his prosecutors defend their undercover sting investigation, but he has a demand of his own: that state Attorney General Kathleen G. Kane face cross-examination about her decision to shut down the probe.

In a legal filing Monday, the District Attorney's Office asked a judge to order Kane to give testimony in the case of State Rep. Louise Williams Bishop, one of six current or former Philadelphia officeholders charged in the sting.

If the judge agrees, the stage will be set for a showdown over the controversial case, with testimony from both Kane and her nemesis, former state prosecutor Frank Fina. Fina set the undercover operation in motion before Kane took office.

Up for debate will be Kane's contention that the sting was tainted by racial profiling, an allegation rejected by Williams and Fina.

"Kathleen Kane was the first and only person to claim that this investigation was racially motivated and biased," Kathy Martin, a top deputy to Williams, said Monday. "And she should be the first person, if she believes that, to come to court and testify under oath."

In the sting cases, Fina struck a deal with an accused thief and registered lobbyist in which prosecutors dropped charges that the lobbyist stole from a program to feed the poor. In exchange, the lobbyist agreed to wear a wire and try to ensnare corrupt politicians in his political and social circles in Philadelphia.

Of the six defendants - five state legislators and a Traffic Court president judge - caught on tape accepting cash or, in the judge's case, a $2,000 Tiffany bracelet, four have pleaded guilty. Bishop and another state legislator from West Philadelphia, Vanessa Lowery Brown, are fighting the charges.

Prosecutors say Bishop, 82, one of the longest serving legislators in the Capitol, pocketed $1,500 in three cash payments, declaring on tape, "That's a great help. That's a biggie," in accepting the last one.

Brown collected $5,000. During one exchange, in which the lobbyist gave her $2,000 in an envelope, she said, "Oooh, good looking! . . . Thank you twice!"

All six defendants are African American.

As The Inquirer disclosed last year, Kane, the first Democrat elected attorney general, inherited the sting when she took office in 2013 and shut it down almost immediately, burying her decision under a court seal.

She brought no charges and did not notify state ethics officials in Harrisburg that the legislators, all Democrats, had taken cash but not reported it on their required disclosure forms.

Kane said the sting was poorly run, even "half-assed." In her most incendiary allegation, she contended that the investigation was driven by race - and that it was even titled "the Black Caucus investigation," a name that Fina has said was Kane's invention.

Accepting a dare from Kane, Williams resurrected the cases. Along with charging the six, the grand jury he assigned to the case issued a harshly worded report rejecting the idea that the investigation had a racial agenda.

Bishop's lawyer, A. Charles Peruto Jr., has cited Kane's criticisms in a bid to have the case against Bishop dismissed. He won a ruling last week from Dauphin County Judge Scott A. Evans that Fina and the sting's street agent, detective Claude Thomas, should testify at a hearing Dec. 16.

Fina oversaw the sting while a state prosecutor under Kane's predecessor, overseeing a string of corruption cases. Thomas posed as the driver for the undercover operative, Tyron B. Ali, while he made 113 clandestine tapes over three years.

Fina is now a prosecutor with the District Attorney's Office. Thomas is a detective there.

Kane has said Thomas told her aides at one point that he had been instructed to target only African Americans. Thomas has denied saying that.

Thomas, who is African American and has twice sued the Attorney General's Office alleging discrimination, has said he would have complained immediately had anyone suggested he limit a probe to black targets.

Kane and Fina have been at bitter odds over the sting case since The Inquirer broke the story of the aborted probe 21 months ago. Kane has singled Fina out for criticism for his role, among scores of current and former state officials, in the swapping of sexually explicit material on government computers.

Kane is awaiting trial on charges of illegally leaking confidential investigative material to the Philadelphia Daily News in a bid to plant a story to embarrass Fina. Montgomery County prosecutors say she did this out of anger because she blamed Fina for leaking the sting story to The Inquirer.

Kane's spokesman, Chuck Ardo, said he was not familiar with the district attorney's effort to have Kane called to testify and would have no comment.

Mark Gilson, the special assistant district attorney who led the renewed sting investigation, said Kane's testimony was appropriate because Peruto relied on her statements in his push to have the case dismissed.

"We want to get to the bottom of this," Gilson said. "I welcome a hearing, but it has to be a full hearing. It can't be a political witch hunt."

215-854-4821 @CraigRMcCoy