Nearly caught up now - finished this earlier this week.
From the Blurb:
Meet Timothy Blake, codename Hangman. Blake is a genius, known for solving impossible cases. He's also a psychopath with a dark secret, and the FBI's last resort.
A 14-year-old boy vanishes on his way home from school. His frantic mother receives a terrifying ransom call. It's only hours before the deadline, and the police have no leads.