When you are in the "Otherworld" (you will go there after you die the first 
and second time), the
Germans soldiers almost always get back up after you kill them. The only way 
to make sure they
remain dead is to devour their hearts.
The following is an easy way to keep the zombies dead when you die. Kill 
them with the demon
arm, and throw them off the ledge. Note: This only works outside. If you 
throw them off the ledge
inside a building, they will not die. Instead, they will follow you up to 
the level you are on. You can
also devour their hearts to keep them dead.