On this page of our guide to Sniper Elite 4 you will find out how to murder Schmidt in the first mission of the game - San Celini Island. Our guide presents the best way to eliminate the main target of the mission.
Your main target is a commander located on the other part of the island, in a large mansion. It's best to get there by going around the island from its outer side, from south, and heading west towards the city. The path was described in the previous chapter, devoted to elimination of officers.
Once you pass the city, you will be able to spot a guard on the balcony (M1.10) - watch out for him when moving towards the mansion (or try to kill him). Head to the main gate.
There are two enemies that you should be aware of: one is in the building on the ground floor and the other patrols the area near the truck - it's best to get rid of them and hide their bodies in the janitor's room in the building.
Now take out the soldier in the courtyard, in the north-east part of the building. To get closer to Schmidt, use the corridor on the ground floor, and hide in the bushes, near the entrance to his room (M1.11). When the time is right, you can kill him with a knife and search his body afterwards.
You may also open a safe on the upper floor with a code from Schmidt's documents. However, you won't find anything valuable inside.
Now get to the boat that you can use to leave the island - you may choose the location below the city, or another one on the other side of the island. The path to the former location is easy - just go back the same way you came from the city, and go around it to get to the boat without further problems.