But he offered no promises. Williams said Kane's criticism of the investigation and its key undercover operative since The Inquirer first reported the aborted sting last month may have permanently tainted any potential prosecution.
"If you are sincere in your desire to let other officials evaluate the evidence, you have been free to provide them the full case file at any time," Williams wrote. "Up to this point, you have been doing everything in your power to ensure that my office could never successfully bring charges."
The letters, obtained Thursday by The Inquirer, expose the growing rift between two of Pennsylvania's most prominent Democrats - Kane, the state's top prosecutor, and Williams, the city's - in the wake of the abandoned investigation.
According to interviews and investigative documents, the sting captured four members of the state House and a Traffic Court judge, all Democrats, on tape taking money or gifts from an undercover informant before Kane shut it down shortly after taking office last year.
She has defended that decision and described the operation as poorly conceived, badly managed, and possibly tainted by racial targeting. All of the elected officials who sources said took money or gifts were African American.
Those who oversaw the sting have said it was a solid investigation that was ably executed, honorably conducted, and had no hint of racial targeting.
Frank G. Fina, the chief deputy attorney general who led the investigation, along with fellow prosecutor Mark Costanzo and case agent Claude Thomas, have since left the Attorney General's Office to work for Williams in the District Attorney's Office.
In her letter to Williams on Wednesday, Kane wrote: "Because your office also has jurisdiction over this matter, and because both the prosecutors and the case agent who conducted the investigation now work for you, I again invite you to . . . bring whatever charges you believe to be appropriate."
As of late Thursday, Williams' office said it had not received any response to its request for the sting's case file. A spokesman for Kane did not immediately answer questions on whether her office would send the file.
But even if the documents are turned over, Williams wrote, Kane's recent statements could make the case difficult, if not impossible, to prosecute.
"You began by attacking line prosecutors and investigators as racist because you disagreed with their judgment about the case," Williams said in his letter. "These attacks on the integrity of my office and its employees will make it more difficult for us to bring these - or any future - cases of public corruption."
Williams also complained that Kane has criticized the key informant in the case, Tyron B. Ali, a Philadelphia lobbyist who faced 2,088 fraud counts that were dropped when he agreed to work with prosecutors.
Kane has said the deal raised questions about his credibility in court. Williams and some other prosecutors have said such deals are often critical to successful prosecutions.
In his letter to Kane, Williams noted: "You have repeatedly asserted it was the previous prosecutors who dropped charges against him, when in fact it appears that it was you who did so, and then sealed the proceedings to keep them from public scrutiny."
Kane's office continued raising questions about Ali on Thursday by releasing an accounting of money prosecutors spent on the case while working with him. A list of $91,056 in expenses, first reported by the Pittsburgh Tribune-Review, included $22,100 in "payments to suspects" as well as $8,351 for meals at Philadelphia restaurants and even a $60 bow tie.
Inquirer staff writer Craig R. McCoy contributed to this article.