Some of FTX’s employees in the U.S. knew about the backdoor in the exchange that allowed Alameda Research to withdraw billions in customer funds, according to a Wall Street Journal report on Thursday. The employees flagged their discovery to FTX’s director of engineering Nishad Singh but the problem never got fixed, the WSJ reported, citing people familiar with the matter. The team, who worked for LedgerX, the crypto derivatives exchange bought by FTX in 2021, was examining whether the code for FTX’s main exchange could be used in the U.S when they made the discovery. LedgerX’s chief risk officer Julie Schoening raised the concerns to her boss Zach Dexter, who then discussed it with Nishad Singh, one of FTX founder Sam Bankman-Fried’s closest deputies.