Recently discharges from St. Mungo’s, Sirius went directly to the Ministry to demand custody of his godson, Harry Potter, as was stated in the last will and testaments of both James and Lily Potter. That’s about when the Ministry realises, they have no idea where Harry Potter is. According to the Prophet, they supposedly searched all their records for any mentions of Harry Potter’s living situation after the death of his parents, but came up empty.