Mr. Strauss will mark this debtor in Chapter 3. Head to the marked location north of Strawberry then follow the a trail going uphill to find his camp. Confront him about his debt next.
He’ll then ask you to follow him to hunt an exotic white cougar inside a cave in the nearby mountain. Just follow him until you reach the cave. Make sure to bring your most powerful rifle and shotgun.
Once inside, you’ll find a split path. Holmes will check the left while you go to the right. Take out your lantern then carefully head inside. It won’t be long until you’ll hear gunshots and Holme’s death throes. Head to his location to find his corpse.
You’ll have to kill the white cougar next. The cougar is capable of killing you instantly, regardless of your health gauge. This animal is perfect in stalking you, and even your eagle eye won’t help track it. You’ll also only have a few seconds to react and kill it if ever you see it with your lantern.
One good tactic is to retreat immediately to the entrance and wait there. You’ll have the upper ground and the cougar will not be able to attack you from behind. Stay near the rock outcrop overlooking Holmes’ body. There’s only one path to your left leading to your position so you’ll only need to wait and keep an eye in front of Holmes’ body or the said path. The cougar will show itself which will give you enough time to activate Dead Eye and land the fatal hits.
Once taken care of, skin the cougar and bring its pelt outside. Stow it and bring it back to Strawberry. Sell the pelt to the butcher to get the required money. Collection complete.