Hm. That does bring an interesting point - *is* it rape by deception if you have any form of sex without knowing the person is trans? is this post or pre-op? Does it make a difference? It falls on a gray area.
I think that the victim thought - ok, he obviously likes me enough to let me give him head, maybe I should disclose that I am trans and see where it goes from here. The guy could've felt misled/betrayed and killed in a moment of passion... or is it temporary insanity? I dunno. But as with anything else, it's best to disclose anything you think may be a problem, like how it's generally encouraged to do so with STD/STI's.
Whether it was temporary insanity or a moment of passion, I am glad that justice was served.