As a punishment for murder, Romans often fastened the dead victim to the guilty party. The penalty for removal of the dead body by anyone was death. A cruel punishment, the body would bloat and rot - the stench would be terrible. That is why Paul makes this statement about feeling attached to this dead body (his self) while his new body (the new man in Jesus) seeks to be free from it. If you saw Fight Club, the dual personality applies here quite well.