Interdealer brokers, the middlemen who line up buyers and sellers of securities for banks, are emerging as key enablers in the Libor scandal after three firms paid a total of $2.6 billion for rigging global interest rates. Employees at firms including ICAP Plc, the world’s biggest interdealer broker, and RP Martin Group Ltd., a smaller British competitor, passed on requests from derivatives traders asking rate-setters at others banks to make favorable submissions, e- mails released as part of...