Mass-murder researchers and terrorism experts do not like turning their calendars to April. For them, it marks the beginning of what one calls "the killing season."
Timothy McVeigh blew up a federal building in Oklahoma City in April 1995. Eric Harris and Dylan Klebold killed 13 people at Columbine High School in April 1999. Seung Hui Cho killed 32 students and teachers at Virginia Tech in April 2007.
Waco. The Boston Marathon bombing. A mass stabbing in Pennsylvania.
Over the past two decades, April's significance has become a source of concern for those who monitor hate groups and fascination for academics who study the seasonality of...