That's my guess too. I can' really think of anyone else that knew who killed Matt and had access to the screws.I think Kurt left the note in Angela’s mailbox.
The last two episodes have kept me on the edge of my seat from beginning to end.
Find it unbelievable and corny that google is putting together more clues than Miami Metro Homicide ever could. Yet, still enjoying every minute of New Blood. Makes up a great deal for the massively underwhelming end of season 8.