A therapy problem

At an out-of-state convention I was talking with another therapist who presented an interesting treatment problem.  I had no really adequate answer, and after having been a therapist for 60 years that's at least a little unusual.

His patient told him that many years previously he had committed some terrible crimes.  Without going into detail, the patient stated that he had accepted money to kill several people. More recently he had gotten sober for the first time in many years and had subsequently fallen into a severe depression.  He had become suicidal and been hospitalized.  

His therapist told me that later on in the therapy his patient recognized his nearly unbearable guilt as undoubtedly the driver for his suicidal impulses and depression.  The patient's depressive thoughts were severely self-blaming, and in some ways even appropriate.

Here are the questions the other therapist asked me.  Should he even be assisted in recovering from his depression?  Isn't his guilt an appropriate response to his behaviors?  Is it an appropriate use of psychotherapy to be relieved of the guilt for his crimes?  Is it acceptable to kill people and then expect to be relieved of the psychological cost of committing such awful crimes? Is that even ethical?

I thought a long time before I was able to give the other therapist any answer at all.  After some thought my initial response was that the first and second principle of the psychologist's ethical code is:  Do no harm. Act to help the patient.  There are no exceptions to those principles, and to me there should be none. 

That being said, the other questions are open for your answers.  I'll be glad to hear any comments.