Even if they already had the results and his DNA matched the one that they found on JY's midriff and breasts, it would not prove anything, because it is only partial DNA, so only good to rule someone out. If there is no DNA match and they have nothing else, they will have to release him because I am pretty sure that he will not confess and will simply repeat over and over again: 'I have not seen JY that day'. His lawyer will do the rest.
I quote you on that, though, because you are correct. It is a little bit as if we knew that the murderer had a surname containing the letters A and K, so that rules GR out, and does not rule NUA out, but it does not prove either that it was NUA, because millions of other people also match this partial DNA (even if it was only thousands, or hundreds, or dozens, it would still be impossible to say that it is him, because it could be a brother, a cousin, an uncle, or an unknown twin brother).
In England, though, partial DNA match is taken into consideration:
http://en.wikipedia.org/wiki/DNA_pr...vidence_of_partial_or_incomplete_DNA_profiles
They mean that it cannot be rejected, but they certainly do not mean that it is a sufficient evidence to prove someone guilty.