In many cases, they're continuing to investigate during the period between finding remains and announcing an ID. Certainly, they usually would know pretty quickly who they have, especially if they have familial exemplars for DNA comparison (or dental records). But beyond notifying the family that there has been a positive ID, there's really nothing to be gained by announcing it publicly--and, in fact, doing so could have the opposite effect. If the killer knows they've found the victim, they might run.
Of course, it's possible that announcing publicly could generate leads (due to the location of the remains), but really...in a case like this, with the body found in a remote area, who besides the killer(s) and/or his or her or their accomplices is going to know anything of value?
The other thing is, sometimes the family member(s) of the victim are persons of interest in the crime (not saying that's the case here), and that might also result in LE keeping an ID a secret---again, to give them more time to investigate and not spook the suspect/POI.
One thing I've noticed, is that as soon as the ID was announced the second week of March, all of the little comments going back and forth between the Twitteridiots have dried up. Skylar is not even mentioned...except for a couple of holiday shout outs (on Easter, no less). Sure, maybe they smartened up all of a sudden and realized that social networks aren't the place to be so blasé about the murder of a close friend that you were among the very last people to see alive...but then again, maybe they're spooked by the discovery. Wondering if they missed something when they dumped her...or dropped something...like a hair...that could be the very thing that leads the cops right to them.
