Evil at Heart, by Chelsea Cain
I read these books because they're set in Portland and I got the privilege of hearing Chelsea Cain speak in 2010. I read Evil at Heart when I flew to Denver for a business trip--it was a great airplane read!
Gretchen Lowell is an evil serial killer on the loose, and Oregonians are apparently obsessed with her. Now of course I agree about the insidious influence of sensational media on citizens, but this seemed a bit over the top to me. I have to hope that if Gretchen Lowell were really a true character, she wouldn't have hundreds of admirers and fan clubs.
If you can suspend reality, it's a thrilling read. I will wait a few years before reading the next one though...it's a bit too light--and violent--for my regular tastes!