"Level 26: Dark Origins" by Anthony E. Zuiker

From BarnesAndNoble.com:

"Law enforcement personnel categorize murderers on a scale of twenty-five levels of evil-from the naïve opportunists starting out at Level 1 to the organized, premeditated torture murderers who inhabit Level 25.

But to an elite unnamed investigations group assigned to hunt down the world's most dangerous killers, headed by Steve Dark, a new category of killer is being defined...."