What does Harper discover when he arrives home with Mayeux? How does he react?

When Harper and Mayeux arrive back at Harper's home in the midst of a bad storm, they find emergency vehicles surrounding the house. They go inside to find Erin and a Jane Doe dead in Harper's study. Harper immediately knows it is the work of the same killer. He is upset that she has been killed, but can't help but feel a sense of relief as well because she was planning on telling Patrick and Drewe about their affair.