Book about a serial killer

[hxdiyah]

Ok, I've looked for a while for this book and am considering giving up at this point. I remember getting it for free with my Kobo reader like 5-8 years ago?
The main things I can remember are:

• It's about 2 detectives, one is a blonde female and one is male. One of them is new- I have no idea which


• It's about a serial killer who has been killing girls and leaving like a torso or a head or something behind


• We see a few chapters intermittently from the killers perspective and he is shown as being a taxi driver


• One of the victims is a disabled girl who was last seen in a supermarket


• The killer has been collecting parts of girls to make human dolls, both detectives have been picked up by him at one point where he talks about his dolls


• The detectives both like to sit at the front of the taxi ( no idea why this is relevant )

Any help would be appreciated x