It was for embezzlement.
Richard Whitney was arrested and eventually pleaded guilty. He was sentenced to a term of five to ten years in Sing Sing prison. On April 12, 1938, six thousand people turned up at Grand Central Station to watch as a scion of the Wall Street Establishment was escorted in handcuffs by armed guards onto a train that delivered him to prison.
Be still my heart. This gives me great hope that any number of felonious investment bank vermin might be frog-marched to prison as an approving crowd cheers.
PS His family and brother made good on the money he embezzled, so yes, there were and are some honorable people out there.