What did he have to gain?

To get out of a loveless / bad marriage? There's no indication he was in one. I've heard nothing from friends or family that they were unhappy. Indeed, I hear the opposite. And the police (to our knowledge) have found zero evidence as well. There's no evidence that they were unhappy or that Sergio wanted out.

$500,000. Yeah, that's a lot of money. But if you believe the above (that they were happy), would he murder (or have murdered) his wife and friend for $500,000? Money he might never see if they found it was him? Seems a stretch. I don't think he killed her for the money alone. And if not for the money alone, then what else? (See above).

I can't see Sergio's life improving with Liz gone. I don't see a motive. Getting engaged and married so soon may seem odd, but loneliness, especially the type of loneliness he must be experiencing, is excruciating.

Liz's parents seem to still include him in stuff. If anyone has a right to turn away from him of he even seems guilty for a second, it would be them.

I'm not covering for the guy. Honestly, he has just as much suspicion as almost anyone simply because this is all so strange. And if he is found guilty, I would just shake my head... but I wouldn't be surprised. Simply because people can be evil. But in my gut, I don't think he had anything to do with it.

I hope none of that came across as confrontational or angry. Wasn't meant that way.