I'm a federal prison consultant. Here's how I went from being in prison to helping clients get ready to go behind bars.

Kenneth A Appelbaum.

• Sam Mangel, a former convict, now works as a federal prison consultant.
• He uses his personal experience to help defendants navigate the system and reduce their sentences.
• After spending time in custody, Mangel learned that knowledge is power in prison.

This as-told-to essay is based on a conversation with Sam Mangel, a federal prison consultant with his own firm. Mangel went into the field after pleading guilty to wire fraud...