All of these will be marked on your map once you find the corresponding memos to them. The trick is finding the memos. There are 3 and can be found in the following locations:
Late employee: Once you get into the infirmary after going through a small window, looking for meds as part of the story, take a right and go through the doorway. Immediately to your right on the ground is the memo. This one is a little tricky to find. The marker will be down south by the barn at the jailors residence. If you go behind and to the left of the barn that has the truck in it, you will find a path that will lead you to a fallen tree you can walk down into the valley below onto a frozen river. Follow the river and you will find the guard. He will have a key that opens a lockbox back at the prison. It is under a bed in a building next to the infirmary. The one with the 3 lockers that require keys to open. Opening this lockbox completes this rumor.
Aggressive Wolf: After the infirmary you should have a key that unlocks a door in the prison wall to the right of the main gate. This is your path outside of the prison. When you open the door it leads into a small room with another door leading outside. Behind the door you entered from there is a locker you can search that holds the memo. The area to search will be in the north east of the map. Go to the area and you're looking for a cave. In the cave you'll find a body with a note that completes this one.
Suspicious person: After chapter 1 you will be tasked with restoring power. Following the road from the prison south and west towards the substation, under a tower you should see a truck. Inside the truck on the dashboard is the third memo. The marker will lead you to the south east to the brick layers retreat. Behind the cabin there is a large rock that has a lockbox next to it kind of hidden in the snow. This has a note in it that will mark a prepper stash. The end of this rumor is in that stash.
There is a point of no return once you get detonators but the game will warn you when you reach it by telling you to finish any tasks before returning to the prison.