What exactly was wrong with Oscar Shales and Agent Mahone? Did Oscar ever kidnap Mahone?
Oscar Shales was a psychopathic serial killer who had raped and killed many women. Mahone was assigned the case of Shales. After almost an year of taking the case, Mahone successfully apprehended Shales on his own. However, he could not fathom turning over a hardened criminal like this to the authority and kills him and disposes the body under a bird bath in his own backyard. He uses lye to decompose the body.
As to your second question, no, Oscar Shales had never even come close to kidnapping Alexander Mahone, an accomplished and able federal agent.