No One You Know by Michelle Richmond

Twenty years ago, Ellie Enderlin's sister, Lila, was murdered and her killer was never found. At the time, Ellie had confided in one of her college professors, Andrew Thorpe. He then wrote a best-selling true crime book about Lila's death, even though Ellie begged him not to. Years later, Ellie is in Nicaragua for her job as a cupper (a professional coffee taster and buyer), when she runs into Peter McConnell, who was involved with Lila. They were both promising mathematicians at Stanford. Peter left San Francisco after he was named in Thorpe's book as the killer. After talking with Peter, Ellie believes he's innocent. Their meeting makes Ellie recall her life since Lila's death and how her sister's absence has affected her family. Ellie then decides to delve into the past to try and find Lila's killer. No One You Know is similar to the books of Jodi Picoult, but a bit more densely written.