Sure enough, when Mr. Lucy showed up at Bank Frey’s offices, Mr. Buck said he would open him an account.

Mr. Lucy was impressed by Mr. Buck’s assurances that his bank had nothing to worry about in the American tax-evasion investigations. “I had found what I was looking for,” Mr. Lucy said.

Mr. Lucy said that Mr. Buck arranged for him to get a Matterhorn-emblazoned debit card that didn’t have Bank Frey’s or Mr. Lucy’s names on it. Mr. Lucy was told that, when he needed money, he should call Bank Frey and ask them to load money onto the debit card. He could use it at any ATM.

Mr. Lucy wanted to bring some account documentation back to New York. He said Mr. Buck advised him not to take anything with Bank Frey’s name on it. (Mr. Buck denies giving that advice.) Mr. Lucy took a pair of scissors and snipped Bank Frey’s name and logo off the paperwork.

Back in Manhattan, Mr. Lucy bought a prepaid phone card for his calls to Zurich. He made them from a pay phone outside his apartment building. When that phone was damaged, the only other functioning pay phone he could find nearby was inside the kitchen of a boutique hotel. Surrounded by the kitchen’s hubbub, he chatted on the phone with his Swiss banker.

By the turn of the decade, other Swiss banks were booting their American customers — and handing them glossy Bank Frey brochures on the way out the door.

Mr. Buck, who eventually rose to be Bank Frey’s head of private banking, said he felt he wasn’t doing anything wrong. All the same, he warned one client, Christine Warsaw, against sending banking instructions through the United States Postal Service, she said in court. “No USPS, use fax,” she wrote in a note to herself. Mr. Buck said he didn’t tell her not to send materials through the mail.