As Potter chased after me in the Department of Mysterious I saw such accusation in his eyes. Yes I had killed my cousin his Godfather but what he did next was completely unacceptable. He cursed me with the cruactious curse though I was lucky enough that he couldn't cast it properly. I didn't want to kill Sirius but I didn't want him involved with the battle. That was why I stunned him. I had no idea what that veil was behind him was the Death Veil. Sirius wasn't supposed to die that day. Potter's accusing glare still haunts me today.