Public mass shootings in the United States have become substantially more deadly over time. We document this increase, offer a model to explain it, review supporting evidence for the model, and present new findings on offenders from 1966 to 2019. It appears that societal changes have led to more public mass shooters who are motivated to kill large numbers of victims for fame or attention, as well as to more shooters who have been directly influenced by previous attackers. They often spend extended time planning their attacks and are increasingly likely to acquire powerful weapons and develop specific strategies to enhance their lethality.

中文翻译：

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为什么大众集体枪击事件变得更加致命？

随着时间的流逝，美国的公众枪击事件已变得更加致命。我们记录了这一增加，提供了一个模型进行解释，审查了该模型的支持证据，并提出了从1966年至2019年的犯罪者的新发现。看来，社会变化导致更多的公共射击者愿意杀害大量成名或受关注的受害者，以及受到先前攻击者直接影响的更多射击者。他们经常花更多的时间来计划自己的攻击，并越来越有可能获得强大的武器并制定具体的战略来增强其杀伤力。