Mark has done this work too long to be showing what looks like disrespect to LE and hitching his wagon to Billie in this way. He has always been about the parents having to clear themselves, in any way they can, first. And yet Billie has not done that, LE certainly has not ruled her out and at this point, at least, I can't blame them. She hasn't passed a polygraph and spends much of her valuable airtime trying to defend Shawn, who has been named as a suspect for legitimate reasons, even if you only count the pings and the job quitting and being the last one to see her, nothing else.
I have watched Mark on NG and other shows for years and have never seen him behave in this manner. It is very confusing and kind of disturbing to me.