I assume you have access to the same information the rest of us have.
We know they were married for nearly 6 years before he left.
We know Islamabad is a tough Embassy and she would have had to provide a ton of evidence about the validity of their marriage.
How do you know he married her for a green card, yes he left her not exactly unusual, happens all the time.
How is it fraud?
I helped a friend of mine adjust her Husbands status, well she signed it, just easier. They subsequently divorced.