Title: The strange seasonality of violence: Why April is ‘the beginning of the killing season’ - The Washington Post
Headings: 
Obsessed with Hitler
Content: The weather connection
There are no indications that the Tsarnaev brothers were particularly interested in April. They apparently wanted an event where tens of thousands of people would be outside, which generally is not the case during Boston winters. But that raises yet another question about April attacks: Is weather a factor? Experts say yes, but not because more potential victims are outside after the long winter. They point to data showing that suicides, often thought to occur mostly in the dreary, socially isolating winter months, actually spike in the spring, starting in April. There is debate about why, although the prevailing explanation is that the increase in sunlight improves mood and energy just enough for suicidal people to make plans and follow through. “They can muster the energy to do something,” said Lankford, the Alabama professor. The timing of the suicidal spike is important, experts say, because many mass shootings and other violent attacks are thought to be a form of suicide among the socially isolated. Harris and Klebold killed themselves.