Hello, Wenchie. I happen to feel that the intruder theory is more likely, so I will respond.
The ransom note is generally considered to be a fake, a prop. FBI profilers said that because of its long length and varied content, it differed from the type of note usually seen ( short and to the point) and was likely a fake. The amount of ransom asked was ridiculously low and was an odd figure. This clearly indicates that the writer saw the figure not as a monetary sum he wanted to collect, but as a reference to some other figure. Possible suggestions: 1. the after tax amount of John's bonus, as seen on his check stubs, 2. the number of cases (118) profiled in a popular FBI profilers book about famous cases. 3. a reference to Psalms 118, which includes the phrase "bind up the sacrafice", and also a few more obscure references. IMO, the most likely is #1, because it agrees with John's bonus and is directly connected to the family, and fits the content of the note. Question: if Patsy wrote the note, why would she use the figure of 118,000, an amount that could easily be connected to her knowing John's bonus or having read Psalms 118? Why not use 250,000 which would look like a true ransom demand?
If you would like to read more about the why, a lot of logical ideas are found in posts #156, 163, 173, and #179.