Detective, Criminal. main character is detective woman (or maybe even man), who is solving case in which, serial killer is following steps of criminal book. The detective woman meets author of the book and they together try to find the serial killer.

[Giorgi]

First of all, main character is detective woman (or maybe even man), who is solving case in which, serial killer is following steps of criminal book. The detective woman meets author of the book and they together try to find the serial killer. I don't have anything else, sorry. Hopefully, it's enough

[Lobstergirl, au gratin]

When did you read it or when was it published?
Where and when is it set?
Series or standalone?
Author's gender?
Cover?

[Amanda]

Sounds a lot like the first episode of the TV show Castle.

[0possum]

I thought immediately of I Am Pilgrim. It doesn't quite match though. In the book a guy who works for a secret agency wrote the book. The detective hunts him down and they work to find a killer. It's a really long book with flashes dealing with the middle eastern countries.