He pretended like he didn’t know about an affair because he was lying to them saying that their marriage was perfect. It was also the obvious motive that had made him murderously enraged.
He absolutely knew something was up. but it seemed he couldn’t figure out who it was. Which is worse because in his mind it could be someone in the neighborhood or someone that Suzanne was planning to start a happy new life with. The truth was this was a long distance relationship as friends (eventually friends with benefits) with another married person. The benefits part could only happen a few times when they rendezvous on work trips across the country.
During this few day time period before Suzanne disappeared, there’s evidence someone made dozens of searches in her Facebook account for male friends.
Also he had trail cameras set up, probably to watch the house to see what Suzanne was up to and to watch the area to see if anybody was coming over. On the day she disappeared, even the minutes before she was never seen or heard from again, she was OUTSIDE suntanning in a bikini and communicating off and on with her lover.
In my opinion, one of his trail cameras was perfectly catching her outside chatting with someone in her bikini, happy and giggling, maybe even showing off her bikini or flashing some skin playfully.
So he raced home and grabbed his horrifying tranquilizer dart gun…