A federal appeals court has upheld former Credit Suisse broker Eric Butler’s conviction on two conspiracy counts but ruled that the government should have prosecuted its securities fraud case against Mr. Butler for duping clients into buying toxic auction rate securities in Manhattan rather than Brooklyn.

The U.S. Court of Appeals for the Second Circuit noted that the only conduct that the government cited to establish venue in the Eastern District rather than the Southern District was that Mr. Butler and his codefendant often flew out of John F. Kennedy International Airport in Queens on the way to meet with investors.