“How’s murky,” she said, but Trey shook his head.
A better line here would be “The ‘how’ of it all is murky.”
While the conversational tone fits, sometimes it can be too sparse for a reader to grasp.
The line “How’s murky…” is confusing and pulled me out of the story for a moment, because I thought she was describing how the scene looked, which didn’t make sense. After rereading twice, I realized she meant that what Trey had said in regard to “the How” as being the means by which Hester committed the crimes and the method is murky.