Just thinking about Walsh's diary.
We have not heard any evidence of this, but I do wonder if there are any entries from after the murder ?
Remembering how excited she was at just the thought of being involved in a murder, I would think she might want to add some notes afterwards, noting how well everything had gone.
Perhaps, if she did, then these are the pages that were torn out.
I think that's what she's referring to when she says SW said if I don't write it down it didn't happen.
I do tend to think it was her that contacted her ex Kevin and not SW. Something just tells me that he agreed to say that to help her.