#2 is of course the ideal. I am looking at the outside of that. Not a person born here. They can do a whole tree and the DNA, might not even be the perp. I disagree that it is not time consuming and cumbersome. People every day even have names of their relatives and cant find them. FOR EXAMPLE..DNA belongs to Joe the stalker.. he connects to you. We dont know who Joe the stalker is..no name..just DNA. YOU have no idea who he is. (5th cousin 2x removed). We dont even have a name. Many 5th cousins of yours are running around. NARROWING IT DOWN TAKES TIME. Then, they have a name or a pool of your 5th cousins..now FIND THEM! They may be scattered all over the continent. Then match all their DNA to the sample. I stand by my observation . It's time consuming..MOO
If the person or his parents are immigrants there certainly may be less DNA matches to work with. Of course that depends upon their country of origin. Some new arrivals to the US come from countries where people are interested in DNA testing and genealogy. Like Canada, UK, Australia, Ireland, etc. Then you will have more matches than typical with other immigrants. But say for Asian and Hispanic it would be more difficult, but not impossible.
Keep in mind most immigrants to the US are not the only ones from their families who have come to the US. They have had close or distant relatives in the past who came here. I have never looked at a match list with no autosomal DNA matches. Perhaps they exist but I have not seen it.
So you will always get country of origin, ethnic breakdown, some family names. It gives you some direction in your search. If you do YDNA testing you can also get male line surname.
The whole point of DNA investigative GG testing is to find a needle in a haystack. You are searching to find the one person on the planet who matches this DNA. You do it by analyzing the DNA and the DNA matches. Of course we can find out who that person is by looking at the match list family trees.
It is science, you triangulate the DNA amounts with the matches family trees. And you can get a name, birth location, parents, grandparents, etc.
When you do adoption searches of course you can find the biological parents even if you do not know their names. You narrow it all down science wise until you have a short list. Then narrow that down to one person.
It is science, not a guessing game. Well it is a complex process but certainly there are more projects more difficult. I have been constructing family trees for myself and others for over 20 years and can do it in my sleep. And doing genetic genealogy for at least 20 years and can do that in my sleep too. And it is only a hobby for me. The people who make a living at it are most likely way more competent than I am. And yes most jobs take time. Sometimes if you get a close match it takes an hour of your time. No close matches it takes longer and is more work.