Your animal instincts tell you to flee but the body and envelope could be the only things you'll ever get that will give you some leverage over whoever is doing this.
With that thought in mind you grab the envelope and slip it into your pocket before examining the body. It's a man is his late thirties, balding and a little overweight. Nothing about him seems out of the ordinary. As you lean over to get a better look, you nice a set of keys on his belt as well as an electronic pass card tucked into his shirt pocket. In this light you can't tell if either the keys or the card are marked or labelled.
The sirens are getting louder. You don't have much time before you get caught stooped over a corpse.