Speaking from a married persons perspective, I'd be frantic. I sure wouldn't take the time to get plane tickets out of the country without telling anyone what happened. Did they figure out if he bought the tickets before he found his wife and child dead?
Thats the first question I'd be asking if I were a jurror.
Strange behavior indeed. Even if he didn't kill them, he for sure had to know SOMETHING was going on if their relationship was as close as the defense makes it out to be.