Actually this is not completely accurate....not all plea agreements involve being or as well rewarded as delacao premiada might be. It is really "reward for squealing" or "ratting on someone for one's own benefit" or "turning state's witness." In a project I worked on, our team struggled with this term. The translation must convey some of the "sleaziness" associated with this term as used in Brazil (in the Waldomiro Diniz case, for example). Someone may have a better idea....