We Are All Guilty Here by Karin Slaughter
Emmy Clifton is a cop in small North Falls, Georgia when 2 teenage girls who are best friends go missing on the Fourth of July. Madison, one of the girls, had tried to talk to Emmy before the fireworks celebration but Emmy had just had a public blowout with her husband and told Madison she couldn't talk right then. Which caused great guilt in Emmy when Madison and her friend disappear soon after. Emmy's father is the sheriff and together they follow the clues and arrest someone. Then 12 years later, another teenage girl disappears right after the man they had arrested got out of prison. And so it begins all over again. There were some good plot twists near the end. But be warned that this is a very dark story.