Dottie is murdered at Ellingham Academy

In Truly Devious by Maureen Johnson, true-crime aficionado Stevie Bell is ecstatic to be accepted into the prestigious Vermont boarding school; not just to get away from her overbearing parents, but to solve the cold case of mysterious murders that happened there. An innocent student, Dottie, was killed in the observation room on April 13, 1936 as the killer made their escape with the school founder's wife and daughter. But not before leaving a terrifying riddle about all the ways to murder them...