The other researcher you're referring to, an eccentric old scientist living in Paseo somewhere near Rolf's house, was essentially the guy who started all the trouble. He was the one who deemed Nei/Neifirst a failure and tried to get rid of her and when she escaped, he put a bounty on her head, which is what first got Darum onto Nei/Neifirst's case. (and the guy turned out to be both bloody persistent and without scrupules) When, in the text adventure, you make Nei speak to him, he recognizes her ears, but later says she's not the one he's seeking. (that'd be Neifirst, presumably)
I believe, near the end of the adventure, Nei listens in on a conversation between Darum and the researcher, with the latter saying he's calling the whole thing off. (the fact two of his former collegues lost their lives over this thing might have given him conscience issues) Darum, of course, doesn't accept the fact he's not getting paid and shoots the researcher, then leaves to look for cash elsewhere in the house. With his last breath, the researcher apologizes to Nei and then dies. (funny thing...if you leave the house through the back door, then walk all the way around and enter through the front, the researcher is alive again...obviously you end up in different "game rooms") Nei leaves and runs into Darum again who decides that even though she's no longer worth a bounty, he'll just kill her for causing him the trouble. Nei can hold him off for a while, but eventually Rolf (at whose house she rested earlier) intervenes and takes Nei home.
Neifirst isn't really mentioned by name anywhere in the adventure and while at first the researcher says that Nei isn't "the one he sought", he later apologizes to her as if she WAS the one born in that bioplant experiment under his supervision. (obviously, in a way, she was since she was part of Neifirst at that point)