The idea is all J.K.'s.
I knew you would hurt me, I knew it, but decided just once to follow my heart instead of my head. I should have known not to trust you, I did know. The moment you told me that this wouldn't work was the moment I could no longer feel. You took that from me, Remus, feeling. There was nothing inside me except pain and anguish. But that was better than this dull, persistent ache, deep in me. The coldness, the emptiness, it's worse than the pain.
At least then I felt human but now, now I know what its like to be truly numb. I know there is only one way to fix this. I came to my epiphany when I saw you, crying over your dead daughter, comforting your wife. I was happy for the first time in years. And I realized, with you sad, I became truly joyful. It was then that I started to kill. It gave me the feeling back. I was human again. I still remember my first; Lavender. I never liked her. She was mean, promiscuous, a whore. She took Ron from me, my first love. I was jealous. So I killed her. The power, it coursed through me as I saw her pain filled eyes, staring at me, pleading with me as I crucio-ed her. For a moment I felt guilt, and then I remembered you, what you did to me, how you would feel when you found out this was your fault. And I finished it; she was dead, and I was happy.
After Lavender, my killing became more frantic. Luna, Kingsley, Bill and others, even random muggles on the street, all of them began to run together. I no longer felt that guilt, but the power, the ecstasy, also started to fade over time. I found killing no longer gave me pleasure, but I was addicted. I was on my own kind of heroin. I decided to go for my final murder, and then I would be free of this emptiness. So I killed you and your family. I even went to your's, Nymphadora's and your son's funeral. It was beautiful, especially when I got to stand up and tell how sad I was, that this was truly heart-breaking for me. How Tragic.