Gibson, 43, was asked to drive the vehicle, which had been equipped by the FBI with video surveillance equipment, to the narcotics unit's headquarters.
Sources said Gibson "lit up like a Christmas tree" when put in a dark room after allegedly taking the chemically treated cash.
Several fellow cops had expressed concerns last spring that Gibson, a 17-year veteran, had been stealing money, clothing and other items during investigations, the sources said.
No charges have been filed.
Ramsey said Friday that he believes the District Attorney's Office will review the case.
Richard DeSipio, Gibson's attorney, said Gibson is innocent.
He said Internal Affairs investigators told him Friday that they hadn't reviewed the video.
"I literally almost fell out of my chair," DeSipio said. "You're asking this man for his badge and gun, and you're not going to pay him based on a video you haven't seen. It's bizarre."
When told of DeSipio's claim, Ramsey said: "I've seen the video, and it's enough to sustain the allegation."
Gibson's wife, Katherine, works as a deputy attorney general in Philadelphia. She told the Daily News last month that the couple had separated.
On Twitter: @dgambacorta