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I know how some of these are done (to an extent):
you can tell the persons diet by things left behind. There are biological indicators on things you eat, for example I know someone who could tell what your typical diet is based on your hair (i think this requires a lab though).
Injury would affect ones movement, and thus the trail, this may also hint on the nature of the injury. also if there is a trail of blood the way it is distributed may give you a general idea of the nature of the injury.
as for how long its been. if the ground is muddy water fills in the foot print, this is sometimes a slow process, and thus the amount of water will tell you the time. It should be noted different types of mud would probably have different time indications. also i heard that if you break a twig, the part that is newly exposed slowly changes color, I assume how long this takes and the maximum color change would vary from plant to plant, but if you step on a twig he maybe able to use this to get general idea of how long its been since you have been here. also odors dissipate so if this guy is tracking by smell, has a good understanding of how strong it is when its fresh, and how long it should take to dissipate (probably depends on oder and environment) then that can be used to date too.
asphalt is easy, if you have the nose of a dog.
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