Complex sentence: In his book Moss said that he had been interested in a career with the FBI; he reasoned that gaining the trust of a serial killer, possibly learning more about their stated crimes or unsolved murders, was a way to distinguish himself as a job candidate.
Split into simpler sentences: In his book Moss said that he had been interested in a career with the FBI. He thought that gaining the trust of a serial killer, possibly learning more about their stated crimes or unsolved murders, was a way to distinguish himself as a job candidate.