“Obviously Mr. Domingo’s team was not in favor of releasing details of the allegations, probably for different reasons,” Mr. Egert said.

The union had planned to release only its top-line conclusions, which said, somewhat vaguely, that Mr. Domingo, 79, had “engaged in inappropriate activity, ranging from flirtation to sexual advances, in and outside of the workplace.” But before it issued the findings, The Associated Press reported that the investigators had spoken with women and witnesses who described unsolicited kisses on the mouth, groping, late-night calls and pressure to have sex.

When the conclusions of the investigation were announced, Mr. Domingo issued a statement saying that he accepted “full responsibility for his actions” and was “truly sorry” for the hurt he had caused women. But less than 48 hours later, after some European arts organizations cited his apology as a reason to cancel or re-evaluate his coming performances, Mr. Domingo amended it. “I have never behaved aggressively toward anybody, nor have I ever done anything to obstruct or hurt the career of anybody,” he said.

The union began an inquiry to find who had leaked information that the board had agreed to keep confidential. In his resignation letter, Mr. Schultz, a baritone, said that he had provided it to The A.P. because he believed the union’s lack of publicly available details about what Mr. Domingo had done amounted to a betrayal of the women who had been harmed.

“Rather than allowing the details of the investigation to be made public, the union entered into a deal with Domingo which protected his reputation, and has allowed him to continue to assert publicly that he did not aggressively sexually harass women or harm their careers,” Mr. Schultz wrote. “The details of the investigation, had they been made public, would have demonstrated the falsity of his denials.”