I am not sure that they would have had enough time to do that. DNA testing takes about 3 days if the sample is put at the top of the list. He was arrested on Wednesday evening, and arrived back in Virginia on Friday at ~5:45 PM. DNA testing would have started then, and would have to run over the weekend.
In any case, that would not be necessary since they would have been able to get DNA from his home and car, they would not need him in custody, although to prove that it actually was him they would need a sample from his person.
I think that if they had a direct DNA match they would have arrested him immediately for murder in the MH case and rape in the Jane Doe case.
So, either this forensic evidence relates to something else, or they have not confirmed it yet.
I am not sure why they would feel the need to release this information now, since it doesn't help their case to do it at this point.