How do you build a proper mystery in a high-tech setting?

Find the half crazy hobo who refuses augmentation and is the only witness.
But because he doesn't have augs or ID (or a SIN or whatever) all you have to go on is the briefest glance of him in the corner of a camera.

Robots, clones, frankensteins, Dr. Moreau hybrids, aliens, future vampires, different aliens, humans that turn out to be robots, more aliens, frozen people from the early 21st century