What is the author's style in In the Belly of the Beast: Letters from Prison by Jack Henry Abbott?

Abbott is speaking from the perspective of a state-raised convict, a long-term inmate who has seen all aspects of prison, including maximum security facilities, psychiatric facilities, and solitary confinement cells. Abbott makes the distinction between the short-term prisoner and someone like himself, who has been in and out (mostly in) of prison since he was twelve. Abbott feels that the state-raised convict is more qualified to speak about the essence of prison than someone who has only done a few years, for the true effect of prison on a man's body, soul, and mind only manifests itself after perhaps five years or more.