The animals that can kill enemies are: Bears, bobcats, cougars, and wolves. It has been reported that a fox or an elk can also kill an enemy for you to gain the achievement.
There are scripted events in the Frontier area where one of these animals kills an enemy. They have somewhat fixed locations. Go to the Packanack hunting zone on the western part of the map for the best luck. Try to find the restricted area (highlighted in red). Go up a hill to the west and you will encounter several bobcats, as well as two hunters. You may not be in open conflict with any of the hunters or animals or they will not attack each other. If this happens, run away. Sometimes a group of enemies are walking on a trail and you can attack them and run to an area high in "predator" animals. Run off and then circle back to follow them and you could have a chance to see them come in contact with an animal.
Predators are Bears, Bobcats, Cougars, Wolves, Foxes. There are a bunch of scripted events in the Frontier area where one of these animals kills a hunter. They have fixed locations and can happen at any daytime. Go to the Packanack hunting zone on the western part of the map. There is a road going from north to south. Follow the road until you come to a restricted area (highlighted in red). Go up a hill to the west and you will encounter several bobcats, as well as two hunters. You may not be in open conflict with any of the hunters or animals! Otherwise, they won't attack each other. Don't shoot or harm the bobcats, they might run away. If you cannot get this done on the first try then get yourself killed and everyone will respawn. Just wait
Pretty easy achievement. One way to get it: attack a guard in an area with predators nearby, run away and he will follow. Hide in the grass or climb a tree and wait for him to search for you. Once he gets spotted by a predator they will kill him.
In the west-southwest area of the Frontier near an enemy camp, follow some wandering guards around and eventually a bobcat jumps out of the grass and pounces a guard in the head. His partner shoots in a futile attempt to help, but too late! He dead! Bobcat gone! Funny!
heres my little guide: http://www.youtube.com/watch?v=WIjnBpc0vrM
check where i was on the map in the video, i must of killed about 10-15 wolfs in this area, find a guy and get the chase, don't kill him, the wolfs will not attack him if your still being chased, they will just run off, so hide until clear then follow him and then watch them kill him.
I managed to get this accidentally, didn't even see the guy die, the achievement just popped. This was the one I wasn't looking forward to trying to get because it seemed too random so I am glad I got it.
OMG i got this one by pure accident and luck, while i was trying to complete the hunter challenges it just popped up. At first i thought my controller disconnected but then it said 10G eye witness. One of the harder achievements i would think. Got it in Troy's Wood btw.
I got this one while doing the hunting side quest to kill a bobcat..on the way there, there were a lot of random guard posts on the way with wild bob cats near by..I just waited in the bushes when I heard a growl and shots fired..you don't actually have to be able to see it on screen as long as you in a close enough proximity you should get it.