Normally, Ramsey said, the department would handle such theft allegations internally, but given the "obvious sensitivity involved," he wanted the case investigated with the discretion and resources of the FBI.
"The fewer people aware, the better," Ramsey said.
The three-month investigation into Gibson's alleged misconduct concluded Thursday morning when Gibson pocketed $140 from a car wired with surveillance cameras during an FBI and Internal Affairs sting operation.
Under the belief that a drug arrest had just been made in the car, Gibson was asked to drive it back to a narcotics field office so a search warrant could be obtained. Investigators had hidden $400 in marked bills throughout the car, sources said. Gibson had no authority to search the vehicle, Ramsey said.
After Gibson dropped the car off, investigators found about $140 missing, which they found on Gibson.
Neither Mayor Nutter or Corbett had prior knowledge of the investigation, Ramsey said, and were not told of the matter until the sting was conducted.
Ramsey briefed the mayor personally. The mayor then put him in touch with Corbett's chief of staff. Ramsey said he did not speak to Corbett personally.
Internal Affairs should complete its investigative report by late next week, Ramsey said.
"Then I will take what I believe to be appropriate disciplinary action," Ramsey said. "Termination," he said, "certainly falls within the range of possible penalties."
Once the department completes its investigation, the case will be forwarded to the District Attorney's Office, which will decide if Gibson faces criminal charges. Gibson has been placed on administrative leave.
Tasha Jamerson, spokeswoman for the District Attorney's Office, said her office could not comment since it had not received the results of the investigation.
Twice in his 17-year career, Gibson has been investigated by Internal Affairs after citizens lodged complaints against him, including a 2009 incident when a Kensington man said $513.55 went missing after Gibson and other narcotics officers searched his home.
That allegation was not substantiated, according to department records.
In 2010, Gibson was exonerated after an allegation that he made a false arrest.
Gibson and Corbett's daughter, Katherine, married in 2010. The couple have a 1-year-old son, but have been separated for a few months, sources said.
Gibson has at least one other child from a previous relationship, police sources said.
Katherine Corbett Gibson was hired by the Office of Attorney General in 2012. She is a deputy attorney general assigned to the Philadelphia office.
Before that she was a prosecutor with the Habitual Offenders Unit of the District Attorney's Office.
Ramsey said he could only think of one word to describe an officer possibly throwing away a career - and his freedom - over petty thefts.
"It's stupid," he said. "You don't do that to your family. And it has nothing to do with who his father-in-law is. You just don't do that to your family. Period."
Contact Mike Newall at 215-854-2759 or firstname.lastname@example.org.