Kane has said she closed the investigation in part because prosecutors had made an unduly lenient deal with the case's undercover informant, dropping 2,088 charges against him in a massive fraud case in exchange for his cooperation.
That, she said, rendered his credibility "horrendously tainted" and would have prevented prosecutors from winning in court.
Williams blasted that decision. "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," he wrote. "As a DA, 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."
Adrian R. King Jr., Kane's first deputy attorney general, declined to respond to Williams' assertions.
Kane has said the sting investigation was poorly conceived, badly managed, and possibly tainted by racist targeting of African Americans. She also said the undercover operative, Tyron B. Ali, had been given "the deal of the century" by Frank G. Fina, the chief deputy attorney general who led the investigation.
Williams spoke out in defense of Fina and Claude Thomas, who served as the operation's lead agent. Both now work for Williams.
Fina and Thomas, he said, had excellent records of prosecuting corruption, targeting Republicans and Democrats, blacks and whites in some of the most high- profile cases in recent state history.
As for Kane's suggestion that the sting investigation may have been tainted by racism, Williams wrote: "I am offended. I have seen racism. I know what it looks like. This isn't it."
Of Thomas, Williams said, "Like me, he is a black man.. . . He has absolutely, unequivocally denied that he was asked to, or agreed to, engage in such reprehensible conduct. . . . I believe he is telling the truth."
In a separate op-ed submitted to The Inquirer for publication Sunday, Fina mocked Kane for her decision to request to meet with the editorial board of The Inquirer on Thursday, only to arrive and decline to address the board or answer any questions. She did so upon the advice of her newly hired lawyer, Richard A. Sprague, who accompanied her to the meeting.
"I have not retained an attorney to advise me to speak, or to remain silent," Fina wrote. "I am an attorney."
Fina called for a televised public forum at which he and Kane could debate the merits of the investigation, which Fina said had been conducted "honestly, ably, and with integrity."
Thomas also sent a statement to The Inquirer on Friday. In it, he vehemently rejected any suggestion that race played a role in the investigation.
"The assertion that I/we targeted African Americans is unequivocably and blatantly false," he wrote. "I did not target any persons by race, ethnicity or political affiliation."
As The Inquirer reported last week, Fina began the investigation in late 2010 in the final months in office of Attorney General Tom Corbett, a Republican. When Kane became attorney general in 2013, she ended the investigation. No one was ever charged.