This is a mechanic I'd really love to have in Dayz. I think it's pivotal that a tracking mechanic be added. Not only for the sake of realism, but for survival and tactical arrangements as well as complex ways of handling situations.

Picture this - If someone gets shot, you may be able to see drops of blood on the ground where he walked, but not have it so obvious that you get right to the person. Also, by investigating the blood, maybe with a sampling kit, you could tell how long ago the person bled, and how dry or wet it is so you know if someone is close or was there a while ago.

Also, other remains, maybe, such as crumbs [ if bread was added ], parts of clothing [ ripped clothing if someone was attacked with a sharp object ], car tracks, footsteps [ however this may be harder to implement correctly ],
shell cassings, empty food cans.

Maybe even mud tracks if your shoes get wet.

Investigation would mainly be the intuition, the experience and information given to you by what you find a body has experienced. A shot, and if so, which bullet, and you can get it out by having a pair of pliers or some medical knife.

It's these little quirks that add so much to the game and how you need to think through where you go and how you find someone. Imagine tracking someone or knowing you could be tracked, making the game even much more rivetting.

Survival would take a whole new angle.