Like a lot of us, I have listened as Kathleen Kane, the attorney general of Pennsylvania, has cycled through what are, in my view, escalating excuses for her refusal to pursue evidence of political corruption. I've watched as she publicly attacked respected career prosecutors and investigators in a desperate attempt to absolve herself. I've made few comments to date but believe it's time for a more detailed response.

I will start with the explosive charges of racism Kane has bandied about. As the first, and only, elected African American prosecutor in Pennsylvania, I am offended. I have seen racism. I know what it looks like. This isn't it.

Let me tell you first about the chief investigator in the case, who has been accused by Kane of taking orders to "target" black officeholders and ignore white ones. Like me, he is a black man. He works in my office now.

He has absolutely, unequivocally denied he was asked to, or agreed to, engage in such reprehensible conduct. He says he did what he has always done as a law enforcement officer: follow the evidence where it led. I have looked at his record, and I have looked in his eyes. I believe he is telling the truth.

What is the evidence to the contrary? The attorney general has said, repeatedly, that she has two witnesses to whom my investigator supposedly confessed this alleged racial bias. Really? Who are they? Why hasn't she identified them? Let us look into their eyes.

If the attorney general supposedly determined months ago that former members of her office who are now members of my office were guilty of "serious ethical and legal issues," why didn't she bring that to my attention? Why didn't she report it to any appropriate authority? Why did she make her accusation - by way of a news release, late on a Friday afternoon - only after her conduct in this case was exposed?

Now let's talk about the prosecutors whom Kane has attacked as racist. They work in my office now, too. Here's why: because of their excellent records.

These are just some of the people they've successfully prosecuted for political corruption - Bill DeWeese, John Perzel, Brett Feese, Brian Preski. The entire leadership of the Pennsylvania House, Republican and Democratic. Every one of them white. And that's not because anyone was "targeting" white politicians. It's because they followed the evidence where it led.

That's why I hired this team. Because they get the job done. Because they have the courage and talent to uncover political corruption, and to put the wrongdoers where they belong. Not everyone does.

I also have to address another conspiracy theory advanced by the attorney general. She says these career prosecutors are just out to get her. She says they were mad at her because she criticized their work on another high-profile case: the investigation of Jerry Sandusky, a former coach at my alma mater, Pennsylvania State University.

Kane alleges that these prosecutors, out of revenge, left her holding a damaged political-corruption case that she was forced to drop, and that they then leaked the story to the press in order to besmirch her reputation. But I have looked into the facts, and they conclusively disprove this charge. These prosecutors didn't leak this story, and I believe that not just because they told me; I believe it because the reporters themselves have said so. Kane should know that too, because those reporters have explicitly advised her office that these prosecutors were not the source of the story.

And there's another problem with this theory: The case files were not in her office when Kane became attorney general. I have been told that before she took office, the files had been given to federal authorities, and they have stated that they never made a conclusion as to the merits of the case. No one left her with a potentially embarrassing decision to make; all she had to do was leave the investigation in the hands of federal authorities. But she didn't do that. Instead, she asked for the files back. And then, after going out of her way to reclaim the investigation, she shut it down.

For whatever reasons, Kane has been largely silent about this important fact. She has repeatedly claimed that it was federal prosecutors who ended the investigation, and that they did so because they concluded that it was without merit. I believe that to be untrue.

Finally, I have to discuss the bottom line - the evidence of political corruption in this case. I don't have the case file myself; Kane has never offered it to me, and she never asked my office to look into the matter.

But I'm familiar with the newspaper reports, and with the attorney general's extensive comments disparaging her own case. Her central complaint, as I understand it, is that she couldn't possibly prosecute, no matter how obvious the corruption, because the witness who recorded the payoffs was offered immunity for serious criminal charges he himself was facing.

In other words, she apparently has electronic recordings of numerous elected officials taking money while promising their votes - and she has to let them off scot-free because she would be incapable of convincing a jury of their guilt?

Prosecutors around the country - local, state, and federal - regularly and successfully bring cases based on the testimony of some very bad men, sometimes even men who have been granted complete immunity after committing multiple murders. But the attorney general of Pennsylvania drops a case supported by hundreds of hours of devastating tapes because the main witness got a deal on a bunch of government fraud charges.

As a district attorney, I think this might be the most disturbing aspect of the whole sordid spectacle. You don't have to be a prosecutor to know this is how it's done. The way to take down organized crime or major drug distribution - or political corruption - is to get someone on the inside, someone who has been part of the enterprise, to give evidence in exchange for favorable treatment. It happens all the time, in prosecutors' offices everywhere - including in Kane's own.

But by attacking this case in this way, Kane has undermined not only this prosecution, but all the other cases carefully built on the same foundation. She has in effect encouraged judges and juries to discredit the very evidence that so often puts the worst criminals away.

I believe she has eroded public confidence not only in her own office, but in the criminal justice system throughout our state. It's time for it to stop.

Seth Williams is Philadelphia's district attorney.