Although it doesn't know the current whereabouts of the art, the FBI believes it might still be in the Philadelphia area. So the agency will launch a publicity campaign, soliciting tips using social media and, within a few weeks, putting up digital roadside billboards in and around Philadelphia, where it believes someone may have glimpsed—or even bought—the art without knowing of the tainted origin. The museum is offering a $5 million reward for a tip leading to the recovery. The theft represents the largest property crime in U.S. history, according to the FBI.