Okay, you have linguistic clues as to who may have written the note. There are always exceptions to rules.
True, but the linguistic analysis, at least the part in question, is trying to build up a profile of the ransom note writer's age, gender and origins; it's not asking the question "Could Patsy Ramsey have written this note?"
We have only a vague idea how the analyst came to the conclusion that southerners are more likely to use "bring" than "take," or how widely held that conclusion is. And there's the issue that at least some of the references readers are given support (though weakly) the RN author being from the Midwest or the North or Louisiana, but not from West Virginia or Georgia because none of the informants from those two states answered 'bring." (That's assuming I understand the DARE entry.)