The most likely is that the killer was merely a deranged and isolated individual.

其中可能性最大的一个传言是杀手仅仅是一个被孤立的精神失常者。

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Three years ago today a deranged man shot and killed 14 people in the main square.

3年前的今天，一个精神错乱者在主广场上开枪打死了14个人。

《柯林斯英汉双解大词典》

An energetic and plain-speaking woman who gives the impression of being untroubled by self-doubt, Holt has little time for the idea that Breivik was just a deranged loner who came out of nowhere.

霍尔特是一个精力旺盛而且直率的女人，她不怀疑自己，她毫不怀疑布莱·维克就是一个毫无前途的神经错乱的孤独者。

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Martin Luther King is stabbed by a deranged woman during a book signing on 125th St. in Harlem.

CNN: On this day in history ...

That said, Garland was able to transform from a somewhat deranged individual into a concert artist who was a magnet for millions, literally in a matter of minutes.

FORBES: Should A Legend Be Challenged?

In another blow, a deranged loner tried to slam a car into an open-topped bus carrying members of the royal family as they celebrated the Queens Day national holiday in 2009.

NPR: Dutch Queen Beatrix Abdicating, Son Will Be King