It all started with a blood drive. Because who would question the motives of one of the legendary senin if they chose to help a charity? Twice a year, the civilians and inactive shinobi of konohagarure hold a blood drive so that ninja injured in battle have a higher chance of surviving. Before it can be used though, the blood must be tested for diseases, type etc. That is where Orochimaru decided to help out. Who was to know if he conducted a few extra tests on the blood he was given? Who was to care, really, in a time of war? The need for blood was great, and if Orochimaru wanted to be more thorough when helping out the efforts, who were they to judge? It wasn't until after the war that people started going missing. Normal people, civilians, some shinobi. Nothing linked them together. There was no pattern. The victims ranged in age, occupation, economic status, social circles, it seemed like they were taken at random. People disappeared sporadically, with no rhyme or reason. It took the ANBU a years-long, in-depth investigation to find the missing link. Every one of the victim's blood had been tested by Orochimaru. Every one of them must have piqued his interest in some way or another by the results of his "extra tests." But by then, it was too late.