Commissioned in January 2013 by Attorney General Kathleen G. Kane and completed by a former federal prosecutor, the full report is expected to be made public soon.
For Corbett, it has the potential to boost or hurt his chances for reelection this year. For Kane, whose name often is mentioned for higher office, it could prove a test of whether the review was worth the time, money, and effort. It's also likely to prove more grist for legions of Pennsylvania State University supporters and fans who have challenged every aspect of the case and its aftermath.
During her 2012 campaign, Kane, a Democrat, repeatedly questioned why the investigation into Sandusky took nearly three years to complete. She also questioned whether Corbett, a Republican who was running for governor during that time, purposely slowed it so as not to alienate donors and potential voters who had a stake in Penn State and Sandusky's high-profile charity, the Second Mile.
Shortly after taking office, Kane hired law professor and former federal prosecutor H. Geoffrey Moulton to lead the probe.
Copies of his findings have been distributed to prosecutors, investigators, and other law enforcement officials who worked on the investigation into Sandusky, the former Penn State assistant football coach convicted in 2012 of molesting 10 boys, the sources said.
The sources spoke on condition of anonymity because the report has not yet been made public, in part because the people mentioned in it are being allowed to review it and attach a response if they choose.
A grand jury judge still must also approve its release.
For her part, Kane has said only that the report is expected to be made public very soon. She declined a request for an interview last week.
Her spokesman, J.J. Abbott, said: "We will not comment on any speculation about the report. It will be released in its full context when all the legal requirements have been met."
Corbett spokesman Jay Pagni said the governor would have no comment.
Moulton's inquiry included interviews with dozens of people, including Corbett and former Chief Deputy Attorney General Frank G. Fina, who headed the investigation. Kane's office also went through the process of recovering scores of internal e-mails her staff believed had been permanently purged by her predecessors.
Those who have read the report said Moulton lays out an exhaustive timeline of the 33-month Sandusky investigation, which began in spring 2009 under Corbett, and examines virtually every aspect of the probe from the moment the first victim came forward to when Sandusky was charged in November 2011.
Throughout the report, details of which were also reported Saturday in the Pittsburgh Tribune-Review, Moulton tackles the key questions that have dogged Corbett since the case became public: Why didn't his prosecutors arrest Sandusky after the first victim came forward, opting instead to put the case before a grand jury? And did Corbett's gubernatorial bid in any way influence the pace of the probe?
Kane made criticism of the Sandusky investigation a cornerstone of her 2012 campaign. She contended that convening a grand jury wasted too much time, and said she would have arrested Sandusky much sooner.
During an appearance before the editorial board of the Times-Tribune of Scranton in September 2012, Kane accused Corbett of "probably" allowing politics to influence his decision-making in the case.
"The reason it was probably politics is you look at all the other factors surrounding it," Kane told the board, noting the campaign donations Corbett had received from people connected to Penn State and the Second Mile, the charity Sandusky founded to help disadvantaged children.
She added: "You don't put a case like that before the grand jury. That was the leadership. Somebody made that decision that they're going to drag that out. Somebody made that decision that they're going to cloak it in secrecy. And I never would have done that."
She vowed to launch a review of the matter as soon as she was elected. That fall, she won the election in a landslide.
Corbett has repeatedly countered that politics played no role in his decision-making, even challenging Kane in late 2012 to bring forward "one piece of evidence, one sentence of evidence, one thread of evidence."
Corbett and others involved in the case have said Kane's position - that she would have arrested Sandusky right away based on one accuser - would have jeopardized the case.
Veteran prosecutor Joseph E. McGettigan, who together with Fina tried the case against Sandusky, said in an interview that in targeting the onetime prominent assistant football coach, investigators were pursuing "a person of great stature in the community, of high profile, who obviously had been doing this for a long time, and had gotten away with it for a long time. As you know, even today there are people who still deny that he did anything wrong."
With such a target, McGettigan said, prosecutors were right to build a case with accounts of abuse from different victims, years apart in age when they testified. The corroborative impact was profound, he said, when the jury "heard these little details from kids who didn't know each other," describing Sandusky's same grooming choices, the same molestations.
By the same token, he said, an early defeat in a quickly mounted case would have chilled other victims, and emboldened Sandusky for decades to come.
In his report, the sources said, Moulton points out that there can be, and were, even within the Attorney General's Office at the time, disagreements between prosecutors on the best way to proceed in a case. But he ultimately is not critical of the decision to put the Sandusky inquiry before a grand jury.
The report does note several areas in the investigative process where the pace could have been quicker, among them issuing a search warrant for Sandusky's home, the sources said. A search warrant wasn't issued until summer 2011, two years after the probe began.
But the sources said the report overall takes pains to take into account both the perspectives of the prosecutors who brought the case and those who criticized it, and makes recommendations to improve the investigative process.
The report will also be closely read because of Kane's tense relationship with Fina, who left the Attorney General's Office just days after she was elected.
One of the top prosecutors who brought the office's highest-profile criminal cases, Fina has been locked in a tense feud with Kane in recent months over her decision to shut down a long-running sting investigation. The sting, launched by Fina, captured several public officials, including four state legislators, on tape accepting payoffs.