The alleged ringleader of a global currency-trading scandal that involves $350 trillion worth of financial derivatives got help from his boss at banking giant UBS, prosecutors in London said Thursday. Tom Hayes’s UBS manager, Mike Pieri, is documented asking for slightly lower interest rates to suit Hayes’s trades in emails presented in court. “We really need some cooperation on the yen Libors [the interest rate] from those who input,” Pieri wrote. A follow-up email noted that he got some concessions from Hayes: “We will be a little bit lower. Every bit helps.” The emails shown in court also demonstrate some internal dissent about the legality of those moves.