A useful technique in killing off German soldiers, when they are in the field of view of many other soldiers, is to do the following:
Check the field of vision for that particular soldier, making sure that no other soldiers can see your unit as well, and then crawl into the darker portion of the field of vision.
After you have done this, wait for the field to pass away, then stand up. The soldier will see as his vision passes back onto you, and will probably say "halt". As soon as he does, go back into crawl mode.
He will come running after you, but if you have crawled away to a safe place, he won't find you. He will stay in that place for a while and then will saunter back to where he had come from.
While he is on the trail back, get your Green Beret,or Marine (or Spy) to go and knife (inject) him. Then clear the body away from the area, so that no other soldiers see it.
This method is best used if you don't want to set the alarm off.