Who were the Nogsim (the task-masers) and who were the Shotrim (the officers)?
Rashi and Rashbam: The Shotrim were Jews whose job it was to force their brothers to fulfill their quota of work, according to the orders issued by the Nogsim, each of whom appointed a number of Shotrim and oversaw their work. 1
The Torah calls his Korban "Ashamo", and afterwards "l'Chatas"!
Ramban (15), Moshav Zekenim: "Ashamo" means 'his Korban'. It is a Chatas, for it is a female.