Those who wish me dead - Michael Koryta

When Jace Wilson accidentally witnesses a brutal murder, his life is changed forever. An ordinary teenager growing up in Indiana, Jace is suddenly forced into the Witness Protection Program and given a new name and history. Taken in by a couple ho run a wilderness program for young boys, Jace finds himself hiking through the Montana mountains, tortured by his memories and by the fear that he'll never be safe again.

The killers, known as the Blackwell Brothers, are two of the most heinous criminals the country has ever known. Jace was the one person to catch them in the act, and he slipped through their fingers. Now they've tracked him down and are making their way across the country, ruthlessly slaughtering anyone who gets in their way.