In January, former UBS executive Alex Wilmot-Sitwell told British lawmakers that he didn't recall the bank's effort to retain a star trader named Tom Hayes, who is accused of being a central figure in alleged efforts to rig benchmark interest rates.

"I don't recall him," Wilmot-Sitwell said at the Parliamentary hearing. "I never met him." He said that Hayes' subsequent departure from UBS "may well have predated my engagement" as co-head of the company's investment bank.