NEW YORK—A U.S. judge on Friday denied Sam Bankman-Fried’s push to get a law firm that advised his now-bankrupt FTX cryptocurrency exchange to hand over documents he says can help him beat fraud charges.

The onetime billionaire, who has pleaded not guilty to charges of stealing from FTX customers and lying to investors and lenders, last month said the documents could prove he relied on legal advice from Silicon Valley law firm Fenwick & West and did not believe he was breaking the law.

U.S. District Judge Lewis Kaplan, who is overseeing Bankman-Fried’s case, in a written order on Friday called the request for a subpoena a “fishing expedition.”

A spokesman for Bankman-Fried, 31, declined to comment.