My boyfriend died almost a month ago. I need to access his e-mails. How to I get his password?

He was a writer and has a lot of his work on there. He also has some very personal e-mails to me that I would like to recover. It has books he was working on, songs he had written, and numerous other items his parents would like to recover. Yahoo mail told me the only thing they can do is close his account. Please, somebody, help me recover his password. I really need this.