See, I'm not really interested in the prequel, because I don't really care how they got to the beginning of the first film.
The mystery of what happened before is part of what makes the first film creepy. I'm not really too fond of over-explanation in situations like this (see Halloween remake, this, proposed new Alien movie(s)). The fear of the unknown can be a powerful thing, and to over-explain everything gets rid of this fear.
Plus I already know how it ends.