Into The Fire by David Wiltse

 FBI Agent John Becker has finally found peace.  Haunted by his history of catching the worst of the worst, the serial killers that killed multiple times, he is not working these days.  In his mind, he is done with the Bureau.  But they insist this is an extended health leave.  John lives with Karen, another FBI agent and her son.  He cooks, plays with the son and lives a life free of stress and horror.

But a former supervisor shows up with the case of two women found in caves, their bodies tortured.  One is the niece of a Senator so the FBI wants the case solved.  John refuses but the man threatens Karen's career and transfers her instead to the serial killer unit.  Blackmailed, John agrees to work the case.

He has been getting anonymous letters from a prisoner and he goes to see him.  Becker hears a tale of a cellmate who brags about killing multiple people, men and women, young and old.  The man, Cooper, is a thug and barely above the line in intelligence.  He has spent his life bulling through, taking what he wants and using his size and strength whenever he meets resistance.  

When Becker goes to find him, he meets a female agent who he requests for the case.  He doesn't talk to her much and explains even less.  Eventually he tells her he requested her because she still has the innocence of a new agent and he needs that counterbalance to his cynicism and his feeling that he has become too much like the men he chases.  Can he find the killer?

David Wiltse is an author and playwright.  His books about FBI agent John Becker are some of the scariest and most tense psychological thrillers I've read.  Becker is a tortured soul who unfortunately is the best the FBI has but he feels that he does the work at the expense of his sanity and that each case brings him closer to there being no difference between the hunter and the prey.  This book is recommended for thriller readers.