Hint 17: Checking George culprit theories

[prof]

So, a three person group, with two adults and one kid? I see, that sounds like it'd explain all the crimes so far, doesn't it?
But hold it! That's actually impossible, too.
Indeed. It's clearly shown that George cannot be a culprit.
Hehe, pretty sharp. The kids can only kill Shannon on the fourth twilight.
A trustworthy purple statement has already proven that George couldn't have been the culprit in Shannon's murder!
That's it. Just one tiny alibi that only works for Shannon's murder. That's what proves George innocent for all of the crimes!
So, we need not suspect George! Which means all of his purple statements can be relied upon!