What If........... When Harry was feeding DD the potion from the cave; DD died ....It would have been Harry that killed DD hince a murder was committed. Unknown to harry @ the time. "It says (HBP) DD was pailer than the inferi. Maybe he was dead then? When they (Harry And DD) got back to Hogsmead Madam Rosmertta said the dark mark just appeared over the astronamy tower momments ago.(ABOUT THE SAME TIME DD SAID KILL ME.) Harry helpped DD take his own life, unknown Harry Murderd DD. When snape came up and seen DD as pale as he was he knew. When DD said," Severus please " It was to do the horacrux spell nonverbally on DD's Inferius body. The white tomb is Harry's horacrux but he doesn't know. DD knew neither could survive while the other lived.......Voldamort doesn't know of this horacrux.