Like the keystone state charm, Susie is the keystone of the family and when she is murdered her family starts falling apart. Jack retreats into his study and obsesses with finding out who killed Susie, Abigail eventually runs away from her family and her grief and Lindsey feels like she has been abandoned.
The charm bracelet represents the charmed life that the Salmon family had led up until this point. They live in a suburb and in a time when murders and rapes did not occur. When Susie, and therefore the charm bracelet, go missing they realise in a violent and sudden manner that this charmed life is a facade. Faced with the tragic death of Susie the family starts to self destruct.