Murder at the High School Reunion — Steve Demaree

In the fifth book in this series, Lt. Dekker gets an advance warning that he might be investigating a couple of murders when two people turn up missing after a high school reunion. When those bodies do indeed turn up, the lieutenant and his sergeant sidekick go to work. They start by interviewing everyone who attended that high school reunion. In their favor is the fact that not a lot of people attended the reunion, but it doesn't help them any when they find out that everyone hated one of the victims, but none of them appear guilty of murder.