I would think that as long as he has not been formally charged with a crime connected with Zahra, LE has an obligation to inform him about the remains found and the probability that it is Zahra. It's also a way to gauge his reaction.
If his lawyer was present I imagine they were limited as to what questions they could ask him, but it's possible he gave them more information voluntarily. For all we know, he may not have been directly involved in Zahra's death or disposal, and one of EB's relatives helped her. I doubt that, but stranger things have happened. As long as he is cooperating, I don't think his arrest is imminent. They will wait until they have sufficient evidence to charge either one of them, IMO. I could be wrong, but it seems they are in no hurry to charge either of them for murder.