Five and a Half Pounds

Brad Miller, an accountant who lived in Van Nuys, California, was shot and killed by a sniper from a hundred yards away. The slug was a .308. It's been six weeks, and the police have no suspects. Brad's mother, Karen, wants Jake to find the killer. In the course of his investigation, Jake discovers that in the past eight weeks, 27 people have been murdered in the same manner--a long distance rifle shot from about a hundred yards out with a .308 slug. He also discovers that all the victims were between 37 and 39 years old, and all of them are members of the California High School class of 1998. What's going on?