It was an unusual situation - a prosecutor explaining why she wasn't bringing charges. But Kathleen Kane seemed supremely confident.

In the spring, in forum after forum, Kane, Pennsylvania's attorney general, said an undercover sting investigation that implicated five Philadelphia officials was marred by possible racial targeting, among many other flaws.

Kane said she knew this because one of her top aides had heard it directly from the sting's case agent. And she said she had contemporaneous interview notes and an affidavit to to back it up.

As it turned out, she didn't.

On Tuesday, District Attorney Seth Williams highlighted this discrepancy and others at a news conference at which he announced the arrests of two state representatives who he said took cash from a lobbyist who was working with law enforcement officials in the sting.

In a rare instance of one top Democratic prosecutor going after another, Williams used the subpoena power of an investigative grand jury to dig into Kane's statements on why she shuttered the sting and test them for accuracy.

He ended up launching a broadside against Kane, saying she had made repeated false statements to justify her decision to end the probe, cited documents that did not exist, and irresponsibly jettisoned a strong criminal case.

Kane closed the case without bringing any charges or notifying the state Ethics Commission that lawmakers had been caught on tape accepting cash. She did so, Williams said, either "out of pure incompetence, to gain political favor, or because of a grudge against other personalities."

Dared by Kane to take up the case she had called unwinnable, Williams also quickly established perhaps the most unanswerable rebuttal: arrests and admissions of guilt.

So far, Williams has now brought criminal charges against three of the five Philadelphia Democrats caught up in the sting, and one of the three has pleaded guilty. The remaining two are still under investigation.

Kane declined to comment for this article.

"Prosecutors disagree all the time on the merits of pursuing various cases," Kane said in a brief statement issued Tuesday. Through a spokeswoman, Kane has declined repeated requests to respond to Williams' specific allegations.

Kane shut down the investigation in 2013, her first year in office. She did so under court seal, so the public knew nothing of her decision until The Inquirer broke the news in March that she had secretly ended the 19-month undercover operation without bringing charges.

The day after the newspaper story was published, Kane told reporters: "I think public corruption is really disgusting. It turns my stomach."

But she said that the case was weak and that prosecutors had no chance of winning convictions. She ticked off a litany of legal problems that she said made the case "non-prosecutable" - from alleged racial targeting to an assessment that the undercover operative would have made a terrible witness.

What follows is a look at what Kane said - and what the public has learned since she first spoke out.

Most explosive, in defending her decision to shutter the sting, Kane raised the issue of race. All of those implicated in the case - a Traffic Court judge and four Democratic state representatives - are African American.

Kane said one of her top agents, Kevin Wevodau, had interviewed the investigation's case agent, Claude Thomas, who, in Kane's account, said senior prosecutors had ordered him to target blacks.

"Our special agent in charge put that in a note, in his case note, and did an affidavit to that effect. . . . That is the evidence we have," Kane said at a news conference in her office April 10.

She added: "When the special agent in charge of the Bureau of Criminal Investigation is asking him questions . . . - taking notes contemporaneously with this statement - we put a lot of credibility into our agent."

But there were no contemporaneous notes, prosecutors said, and there was no affidavit.

What there was, they said, was an unsworn case memo from Wevodau outlining Thomas' supposed complaint of racial targeting. The memo was dated April 14, 2014 - four days after Kane said she had the affidavit in hand.

"She had people create documents after she said she had them," said Assistant District Attorney Mark Gilson, the prosecutor Williams appointed to revive the sting investigation.

Wevodau wrote the memo about 15 months after he interviewed Thomas - and also months after Kane had ended the sting.

The interview took place before Thomas, a veteran of 26 years in law enforcement, left Kane's office last year to become a detective on Williams' staff.

Thomas has denounced Kane's claim that he said the probe was racially driven.

"I never uttered those words or anything near those words. That is a complete lie," he said Friday. "For the entire investigation, race never came up whatsoever."

During his two decades with the Attorney General's Office, Thomas, who is African American, twice sued the agency for racial discrimination.

Had he been ordered to target blacks, he said, "I would have rejected it and immediately challenged it. I would have reported it to Internal Affairs without delay."

Theodore Robinson, a former agent in the Attorney General's Office who joined with Thomas in one of the lawsuits, said he was flabbergasted by news stories quoting Kane as saying Thomas might have agreed to target African Americans.

"Trust me, when I read that, I was just like floored," Robinson said in an interview. "Let me say this: Of all the minority agents in the A.G.'s Office at that time - Hispanics and blacks - Claude would be the last one to whom anybody in the agency would think to propose such a thing. I could not imagine them going to Claude Thomas, saying, 'This is what we want you to do.' He would lose his mind."

Last week, Williams said that even Kane's chief lieutenant doubted the race charge.

Bruce Beemer, Kane's second-in-command, recently testified before the Philadelphia grand jury that he "never for a second" believed the racial allegation and that "absolutely nothing in the case file" reflected a racial focus, the panel said in a report last week.

At a news conference earlier this year, Beemer joined Kane in criticizing the sting and suggested that the five officials who took money or gifts may have been entrapped.

"There appeared to be very little attempt made to ascertain whether or not individuals were engaged or predisposed to wrongful activity before they were targeted," he said.

Smart targeting, Beemer said, is critical to a successful bribery case.

"It helps to ensure that prosecutors and government agencies aren't running around trying to entice people to commit crimes where they would not otherwise be predisposed," he said.

Williams laid out an entirely different scenario last week in announcing the arrests of State Reps. Vanessa Lowery Brown and Ronald G. Waters on bribery charges for pocketing cash.

By Williams' account, the informant who caught them on tape, Tyron B. Ali, simply followed a social and political network that led him logically from one public official to the next. Pointedly, the district attorney noted that Ali was a friend of Rep. Waters' daughter and that she was the one who introduced him to her father. Waters, in turn, put him in touch with other targets.

Moreover, Williams unearthed a 2013 e-mail exchange in which a former top aide to Kane, Linda Dale Hoffa, told a colleague that the sting had "ample predication" and that "no legislator was entrapped."

According to city prosecutors, the colleague - Beemer - agreed.

Waters' lawyer, Fortunato Perri Jr., said it was never easy to overcome the fact that someone took a cash payment.

"An entrapment defense is always a difficult one to mount," he said. "Especially when you have multiple criminal acts, as we have alleged here."

In Waters' case, prosecutors say he put his hand out nine times in all, pocketing a total of $8,750.

When questioned by the grand jury, the veteran legislator admitted that taking the cash was a crime, Williams said. Brown, too, admitted her crime, the prosecutor said.

In attacking the sting, Kane was sharply critical of Ali, the investigation's confidential informant.

She said any good defense attorney would attack the deal Ali had been offered by her predecessors. Ali began cooperating after being charged with fraud in 2009, when he was accused of skimming $430,000 from a state food program for low-income children and seniors.

In what Kane called "the deal of the century," prosecutors dropped the fraud charges in exchange for his undercover work on the sting case."

"You put that CI [confidential informant] before the jury, and his credibility is shot," Kane said at one point. "The only one who can verify those recordings would have been that CI. Because that CI was tainted, those recordings may never have been allowed into court and that prosecution would have failed. No doubt."

Williams, after reviewing financial documents in the case, concluded that the actual size of the fraud was far smaller - less than $100,000.

More important, the district attorney said, Ali was hardly the only witness. The crimes were captured on tape.

Perri, Waters' lawyer, said that no matter how much jurors may dislike an informant, they rarely use that as a reason to acquit - especially when there are tapes to hear or video to watch.

"The most powerfully incriminating evidence the government can present against a defendant is his or her own voice admitting the criminal activity," Perri said.

On Wednesday, the first person Williams arrested in the case, former Traffic Court Judge Thomasine Tynes, pleaded guilty to conflict of interest for accepting a $2,000 bracelet from Ali as the two discussed his desire to win a collections contract from the court.

As it happened, there was no need for Ali to testify at a trial. There was no trial.

Instead, Tynes' lawyer, Louis R. Busico, worked out a deal with prosecutors to drop a more serious charge of bribery and other offenses. He said the decision to admit wrongdoing made sense.

"I don't want to speak for the attorney general and why she may have said certain things. And I surely can't read her mind," Busico said.

"But what I can do is I can listen to tapes. The recording that I heard absolutely made this case one that had prosecutorial merit."

215-854-4821 @CraigRMcCoy