The trial of Jérôme Kerviel climaxed on Thursday, when French prosecutors said the former Société Générale trader should be imprisoned for four years and fined for crimes that led to the biggest single trading loss in history.

The trial is focusing on the extent to which Kerviel, the only defendant in the case, hid his actions from the bank-and how far the bank should be held responsible for its lack of control over him. Between 2005 and 2008, Kerviel made illicit bets worth as much as €50bn ($61.6bn). The bank had a net loss of €4.9bn when it unwound his positions.