The source of it all

"What am I doing? Even if I go on and on here, preaching about family values, you will not understand the concept of family. You don't have one. You killed all of them. Poor guy."

Zero maintained his smile despite the continuous taunting from Samael. Well, he couldn't get angry because one, what Samael said was nothing but the truth. And second, he felt no shame in massacring the entire Moriarty lineage. 

"They were all nuisance," he said with a nonchalant shrug. "But anyway, I did my best, Samael. I tried giving you the option to end this chaos rather peacefully. But alas, it seemed I can't change your mind."

"I hope you will not regret this," Zero added, smiling confidently.