In crime fiction, we have at least three main characters: The hero(ine), the villain, and the victim. We root for the protagonist, despise and possibly fear the antagonist, and...
What about the victim? Should the victim have a face, and be as well-developed as the other principal characters? Or should the victim merely be a slab of meat on a stainless steel table? How much sympathy do we, as writers and readers, owe the victim?
In my novel currently on submission, a body doesn't turn up until the beginning of Act II. The body happens to be, I hope, someone the reader cares about by that time. S/he lived and breathed for the reader--and for the other characters in the novel--but now s/he is gone. Brutally gone.
To me, this leaves a bigger impact than if I had started with the murder and then developed the victim through backstory. I've seen it done successfully both ways, but...
Think Silence of the Lambs. Why did that book work, even with no murder onstage (other than the faceless--no pun intended--guard when Hannibal escaped)? I think one reason SOTL worked was because the victim (who ultimately survived, of course) was as well-developed as the heroine and villain.