Apparently deleting them before wasn't permanent enough.
Previously when you deleted a photo from Facebook, it didn’t always get removed fully. Instead, some photos loitered around Facebook’s system with the possibility that it would later reappear to embarrass. That's a fairly scary thought when you consider some of the photos that people leave up. However, Facebook has resolved this long standing issue thanks to an update to its deletion policy and a photo storage system migration. Removed photos will be in the system for a maximum of 30 days before they are deleted permanently. Not quite as quick as something like Instagram, but at least we can worry less about dodgy photos from a weekend reappearing for a prospective employer’s viewing.