US prosecutors on Tuesday sought to cast doubt on the testimony of the wife of a former Goldman Sachs banker, who is on trial over allegations he helped loot Malaysia's 1Malaysia Development Berhad (1MDB) sovereign wealth fund.

Roger Ng, Goldman’s former chief for Malaysia, is charged with conspiring to launder money and violate an anti-corruption law. Prosecutors say he helped his former boss Tim Leissner embezzle money from 1MDB, launder the proceeds and bribe officials to win business for Goldman.

Ng, 49, has pleaded not guilty...