Of course, obvious questions come to mind when thinking about finding a ransom note like they did. After Patsy began to read it she probably got as far as directions to get $118,000, then panicked. She calls John with the news, then both probably started checking bedrooms, etc. John could have gone downstairs to make a quick check. At this point maybe they read the rest. John might have gone out the front or back looking for cars. Or they could have called the police after the quick house inspection, and began to look closer at the note at that point. It seems pretty obvious that they would check inside and at least look outside the front and back.
This is my opinion, and change is good.