Murder Points a Finger, by David Alexander (epub/Kindle/pdf)
A COP-KILLER WAS LOOSE!
The Cop: "Just find Ellison." Inspector Sanson said, "-- and leave me alone with him in a locked room --"
The Girl: "He used to make me scream and cry when he tore the wings of butterflies, and now -- and now —-"
The Killer: "I have to kill her. I have to kill her now because of you. I'll have to kill you too, of course."