Why would the detective ask him if he had stopped by a dry cleaners on the way home from the desert (for example)? The point is DW did not volunteer the info. Though it is reasonable to expect people to forget details when answering questions. I think the questioning shows how weak the defense case is. Shows how perceptions can differ.
As I prepare this I see that DW made a big point to say how the kids were running all over. I think some more forensic evidence was found upstairs that we will be hearing about.