The Warden and all the Aurors at the prison had to answer questions under truth potion, and other Aurors tracked down where the Snakestone was, during every hour of that night. Those other Aurors were thorough at talking to people and at reading records, so their investigation took a long while. The other Aurors decided that the Warden hadn’t killed those eight murderers, the prison-guard Aurors hadn’t killed those eight murderers, and the Snakestone had stayed where it was supposed to be during the entire night, without being stolen, borrowed, moved or copied. Those other Aurors are sure who did not kill the Death Eaters (the Warden and prison-guard Aurors), but they don’t know who did kill the Death Eaters, or how the murderer(s) moved in and out of the prison. Those other Aurors don’t know how the Death Eaters’ cell doors were opened.