Blood on the Boa

Chloe Walters was the third to drop, swiftly followed by a short lived Abby Turner. It wasn't until the death of the girl sitting next to me on the bus died that I actually got scared by the string of murders in town. Always marked by the bloodied feather of a cheap boa. But why? How is this happening? And how many more are going to die?
And...
how long until the murderer reaches me?