You did not cleanup for the commas. Also I would suggest to lower the text first. Here is a much simpler method:
def prepare_text(text):
lower_text = text.lower()
punctuation = ".,!?"
no_punctuation = ''.join(letter for letter in lower_text if letter not in punctuation)
return no_punctuation.split()
https://github.com/DeadMarshall/codecademy/blob/6f67a46034f5b5584c9f0e26fd028b57f73e80b6/bstinsonMurder%2BMystery.py#L147-L156
You did not cleanup for the commas. Also I would suggest to lower the text first. Here is a much simpler method: