The results of a Credit Suisse investigation into the episode, conducted by an external law firm for the board of directors, were announced on Tuesday. The board was told that the surveillance had found no evidence that Mr. Khan tried to poach employees or clients from Credit Suisse.

The investigation also found that Mr. Thiam and other executives had not been aware of the spying. Because of this, Mr. Rohner said, “we strongly reject any and all assertions made over the last days that call into question the personal and professional integrity of our C.E.O.”

The bank said on Tuesday that James B. Walker, who was chief financial officer for the United States, had been appointed to take over Mr. Bouée’s role. It also said it had accepted the resignation of the head of global security.

After several years of putting its house in order, the bank faced questions on Tuesday about whether Mr. Thiam had been properly informed about the surveillance — or what was happening under his management if he did not know that Mr. Khan was being watched.

“I don’t believe in my own mind, speaking as a board member, that that suggests that Mr. Thiam is not on top of the rest of the organization,” said John Tiner, chairman of the audit committee, during the news conference.

Mr. Rohner said there had been personal differences and “heated discussions” between Mr. Khan and Mr. Thiam that ended in Mr. Kahn’s leaving, but he did not elaborate on their relationship. The investigation, he said, did not find any proof the spying was linked to animosity between the two men.

Still, Mr. Rohner apologized, saying that the results of the Credit Suisse investigation “do not change anything about the fact that the reputation of our bank has suffered in the last few days.”