In summer 2010, Citigroup traders circulated a news report about attempts to manipulate a financial benchmark used to calculate a wide range of interest rate products. One messaged: “GAME OVER.” “[O]h jesus do I want to read this?,” chimed in another, according to a document recounting the exchanges released by regulators.

By then US regulators and law enforcement authorities were deep into multiple investigations into whether top global banks tried to game interest rate benchmarks.