Talk:Slayer's End/@comment-24032096-20170504163940

It was revealed during the events of the case the reason behind Fiona's killing spree:

Many years before, she had a friend named Celia Barnes, a prostitute who died of syphilis at the age of 21. Celia's death had a great impact on Fiona's emotions, and she prompted to kill all prostitutes to free them before contracting the disease.