What I have wondered about him mentioning her is that he didn’t mention her at all in the Paula zahn show. He brought up his dad and according to the dash cam and police reports, he didn’t bring him up at all.
In my state, I have come across many men of Sergio's type. And, one can't always judge them from "conventional" standpoint. They may get exceptionally upset when a partner/friend doesn't answer the phone, and at the same time, for example, not cry at the funeral, and it doesn't indicate any guilt. Some, the smarter ones, may get dangerous as they have unbelievable logical ability, but I am not at all sure that S is in that group. The inconsistencies are normal for humans, it is what your mind focuses on during the conversation.
So, about S. The only thing that would dramatically raise the suspicion for me would be any hint of a side relationship (or looking for one) when he was married to Liz. Or, increasing amount of arguments before her death. But, I don't know if these things existed. If not, he is in exactly the same "47% of women are killed by intimate partner, but 53% are not" group.
Fast remarriage and moving on with a child might indicate that he is not a very strong person and more a follower in his relationships, and his current wife was ready to move on with the new family. The fact that he stayed in the house he shared with Liz for a while might mean: a) either knowing that he wasn't a target, or, b) are we sure that he was really sleeping in the house? Maybe he stayed with dad/friends, trying to organize many things at once? (But sleeping in the house alone would be a concern - many people move out to escape memories).
What really bothers me is that because SB's emotional reaction was "not quite conventional", too much time/energy was spent chasing his alibi, and someone truly culpable might have slipped through the fingers.
Of the two, LB seems to have been more organized and social. How many people were in cosplay, but she rapidly grew through the ranks. She was respected at work. She was active. At the same time, and I can only guess, but she comes across as a smart woman who is not too prone to oversharing. This might have eventually worked against her. But - she has had many circles, her family, her husband, her job, that Legion, friends, past life, something else. It all needs to be gone through with a fine-tooth comb. I am positive that the shooting was not random. But, given how busy the police was during these years (possibly, dwindled in numbers), her murder stays unsolved. And after all, I think, there may be a slight chance of another serial killer at loose, or a "grievance collector" from her past so there is this, too.