Gibson could not be reached for comment Thursday.
Gibson was targeted specifically by the U.S. Attorney's Anti-Corruption Unit, and his supervisors were aware of the sting, law enforcement sources said.
He was under investigation for at least eight months, sources said.
Law enforcement sources described the sting:
Federal agents and police Internal Affairs investigators placed $400 in marked money in a car for Gibson to investigate. The bills were sprayed with a powder used by police in controlled drug busts, and the car was equipped with surveillance cameras.
Gibson was told that police had a warrant to search the car and was asked to bring it back to the Narcotics Field Unit for a search. When investigators checked the car after he did so, about $145 was missing.
Investigators recovered the money after searching Gibson and his personal car. He also had the powder on his hands.
At a Greater Philadelphia Chamber of Commerce event Thursday evening, Gov. Corbett quickly exited the stage via a back door after an hour-long discussion billed as "A Conversation with the Governor," as reporters waited to ask him questions about his son-in-law.
NBC10 reported that Corbett issued a brief statement: "I was surprised and concerned to learn about the allegations regarding my son-in-law Gerold Gibson. Susan and I continue to give our family our love and support."
Gibson is married to Corbett's daughter, Katherine, who works as a deputy attorney general in the Philadelphia office. She started in March 2012 and as of late last year was assigned to the office's Drug Strike Force section.
Before that, she was a prosecutor with the Habitual Offenders Unit of the Philadelphia District Attorney's Office. Sources said the couple have separated.
Contact Mike Newall at 215-854-2759 or email@example.com, or follow on Twitter @MikeNewall.
Inquirer staff writers Angela Couloumbis, Bob Fernandez, and Amy Worden contributed to this article.