But while Profexer’s online persona vanished, a flesh-and-blood person has emerged: a fearful man who the Ukrainian police said turned himself in early this year, and has now become a witness for the F.B.I.
Mr. Gerashchenko described the author only in broad strokes, to protect his safety, as a young man from a provincial Ukrainian city. He confirmed that the author turned himself in to the police and was cooperating as a witness in the D.N.C. investigation. “He was a freelancer and now he is a valuable witness,” Mr. Gerashchenko said.