Hi
Which apartment are you looking for? the vic's friend or the girl?
There is evidence in the room that is needed to be found- have you looked on the floor behind Grissom? (hint).
Make sure you have handed all evidence you got from the hotel to Greg and analysed everything as much as possible- the game is very linear and it might be stopping you (momentarily) from getting the apartment location until all the evidence is done.
Hope that helps!
(if not, post again
)