The stranger is an element of the group itself, not unlike the poor and sundry 'inner enemies'—an element whose membership within the group involves both being outside it and confronting it.
Rule of 7 in research. You can find out anything if you are willing to go seven levels. If the first source you ask doesn’t know, ask them who you should ask next, and so on down the line. If you are willing to go to the 7th source, you’ll almost always get your answer.