You’ll find Dutch and John near Bronte’s Mansion so make your way over to him when you’re ready to begin the mission. Like all missions with a timed objective, you will have to skip cutscenes to stand any chance of meeting the requirement and even then you’ll be cutting it close. As a result of this, consider replaying the mission so you don’t miss out on the story.
Once you regain control, head with John and mount your horse, following him to the nearby graveyard. Dismount the horse and head inside to begin searching for the grave robbers. As you begin heading down, you’ll hear a dog barking in the distance, head to the right and around the back of one of the graves to find it. Continue past the central area of the graveyard and then head around the north of it to hear some more commotion, once again head around the back of a tombstone to find a drunken man.
With this objective fulfilled, make your way to the northeast of the graveyard and investiage the mausoleum when the grave robbers will begin to attack you. While still in cover, quickly activate Dead Eye and ensure you headshot each of the grave robbers. If you don’t score the four headshots for the Gold Medal against these enemies, you’ll have to use a Bow or Throwing Knives in the final part of the mission which will make it a lot more difficult. Once the final grave robber is dead, head to the marked area and search the mausoleum to find the stash.
You’ll be interrupted by Lawmen who have come to investigate the commotion and it’s now clear you need to get out of the graveyard. You’ll need to stay undetected for the Gold Medal and the best way to achieve this is by sticking to John at all times, do this and you’ll avoid detection. Remember to keep crouched while you follow him and hold the [X]/[A] button during cover transition to keep the pace up with John. Once you exit the graveyard without trouble, mount up and gallop as fast as possible back to the Bronte Mansion to complete the mission.