RE: what happened to this deer?
Don't forget to check the leaves of bushes and low trees along the trail, not just on the ground. Blood from a wound high on the deer's body can get soaked up by the fur before it reaches the ground, but it will get wiped onto leaves and branches the deer's furcomes in contact with, usually about 2 feet off the gound.
Hope that it hit the liver, but if the blood was VERY dark, it could also be high in the stomach, or both organs. Either way, the deer will die, and should be dead by now (the next day).
Do the tissue paper thing mentioned above, and get some buddies to help you search the area well with an organized search pattern. Pay particular attention to the thickest growth in the the greneral direction he went, as that is where he'll have wanted to bed.Also, remember to look around you 360 degrees often, as you may see the white of his belly from one angle, but only his well camoflaged back from another. Since it's been 24 hours, watch for scavenger birds. I've read that theycan home in on a dying animal's locationeven before it expires.
He's there somewhere, and he's dead. Just got to find him.
Not an easy task, but possible if you go carefully.
Good luck.