Some day we'll learn the truth, I'm sure of it.  Only a guess, but the logical conclusion based on all of the publically released facts in this case -- is that the mother conspired to have her son was spirited out of the country and sent to live with her extended family in Russia.  Her context of running out of gas was knocked down early on, so she clammed up to avoid giving away any further clues as to the true events that occurred after she left the vehicle.  To find the boy, someone will have to travel to Russia to investigate the family there, which is probably not going to happen unless a private investigator is hired.