In my opinion, GBC will be saying absolutely nothing at this stage; as would have been the advice from his legal team.
The relevance of DNA testing will be interesting, considering there would obviously be a high concentration of GBC's DNA in the house/car and on Allison. It could also possibly be used to "identify" the presence/absence of unidentified DNA.
Just going back to the initial swift reaction from police, and wondering how much access they were given to the vehicles/house early on the Friday morning (before warrants were issued). I'm starting to wonder if it was GBC's reaction (assuming it was similar to that seen on the interview), along with comments from neighbours re arguing) that triggered initial suspicions that morning.
I'm also wondering if the blood eventually found in the car was a significant trace/amount, leading the police to the conclusion that she had met with foul play.
Also wondering if police are still missing the murder weapon.