The Last Place You Look by Kristen Lepionka

Private detective Roxane Weary is hired by Danielle Stockton, whose brother Brad sits on death row for murdering Elaine and Garrett Cook. Brad was dating the Cook's daughter, Sarah, who went missing on the night they died and hasn't been seen since. Danielle is convinced that she recently saw Sarah and wants Roxane to try and locate her. The situation is urgent, because Brad is set to be executed in two months. Roxane retraces where Danielle thought she saw Sarah and also uncovers that Sarah is not the only young woman to go missing in Belmont, a Columbus, Ohio suburb. Could Brad be innocent? Will Roxane be able to find enough evidence to set him free? The Last Place You Look is the first book in the series featuring Roxane Weary. I'm definitely going to read another one.