What crime did the fat convict plead guilty to in court, and why?

The prosecution for the fat convict's case was very willing to work with him during his trial, giving him the option of pleading guilty to a lesser crime - violating the Mann act - or to manslaughter. The fat convict decided to plead guilty to the manslaughter charge because he would be allowed to pass through the back doors of the court house, thus avoiding a confrontation with his very angry accomplice.