I believe he understood my intentions as soon as he saw that I possessed the Invincible. He had done everything in his power to prevent anyone from touching it. Only Albus and Dylan knew the password to take it out of the safe, but it was easy, one night, to convince Dylan to reveal it to me. I touched the Wand days before using it to kill, to make sure it belonged to me, and it chose me. I had confirmation of that when I invoked the Killing Curse.