If you happen to find a body, or anything suspicious of human remains - no not touch anything. You can step backwards in your previous footsteps and immediately notify police. Keep people from approaching until police arrive to secure the scene. If you have no cell contact (areas in West desert) and need to leave to find a phone or get into cell range, make sure you note exact location to report to police. If someone can remain on the scene to prevent people from approaching, and direct police to the area that would be ideal.
It is important not to relay what you have found to any media and let police take care of that.
If you find something you consider evidence - do not move or touch but notify police. You can photograph and note the exact location to report this to police.