Who was the nurturer that injects the smaller twin

Well, if this is from the giver, the boy's father injects the smaller twin. That is why when the giver actually shows the boy what happened during the process, the boy is so distraught. He thought his father was a good person. After that he then realizes that his whole society is messed up and that they kill their own kind if the don't fit in with society.

The answer is the father was relieved, the officer was tired.