Ethics

A colleague posed this hypo, which offers a twist on the classic Stenhach and Belge cases:

A client (a defendant in a criminal case) records a telephone conversation with the complaining witness.  The recording contains very helpful impeachment material, but the recording is a crime under the relevant wiretap statute, because the recording was made without the knowledge or consent of the complaining witness.  The client transfers the conversation to a computer and gives a copy of the file to the lawyer. What are the lawyer's obligations?

There are numerous cases that say that a lawyer cannot take permanent custody of any evidence of a crime.  A lawyer, however, is allowed to examine the evidence.  But what about when the evidence of the crime (in this case, the violation of the wiretap statute) is in electronic form (i.e., the recording), and the lawyer merely receives a copy?  Can the lawyer listen to the recording?  Even more interestingly, can the lawyer retain the copy assuming that the client retains the original and is not advised to delete it or dispose of it?