It may be legal to record the conversation in California, but he can strongly argue that he had a reasonable expectation of confidentiality. Besides, the case would be tried in New York, where the recording may or may not be legal. It would not be difficult to have that tape suppressed. And there goes the prosecution’s case.
Unless the alleged victims are willing to testify, the case rests on the tape and the wife’s hearsay, and the latter is weightless.
Then, if I were he, I’d sue the ever-lovin’ crap out of the wife and the therapist who let this happen. Unless the therapist is a mandated reporter, she can kiss her license goodbye.
New York is a one party consent state so the recording would be totally legal and admissible there. CA is a two party consent state, but apparently there is an exception for seeking to document evidence of a crime.