Blue On Black is a short story by Michael Connelly featuring Harry Bosch. It was originally published on April 19, 2010 and was part of a collection of short stories with a fishing theme called Hook, Line & Sinister.
It was subsequently re-released as a standalone short story on September 6, 2016.
Blue On Black book description
Two women have gone missing, and LAPD Detective Harry Bosch has a strong suspicion that an avid fisherman named Denninger is the culprit.
Bosch needs something stronger than a suspicion to bring Denninger in, but all he has are a handful of photos–prior mug shots and pictures of Denninger posing with his prize fish.
It’s not much to go on, and Bosch is running out of time, which is why he calls in FBI agent Rachel Walling. What she sees in these photos could blow his case wide open.