请翻译 He will kill at the drop of a feather.

这个强盗是纽约有史以来面临的最危险的罪犯之一.“他会信手杀人的,”负责案件的人说.
对 "at the drop of a feather"的英文解释如下：
It may be based on the idiom "drop of a hat" .
This is a saying from the American west,and it appears that Native Americans,apparently,also had a tradition that certain ritual actions be done if an eagle feather falls from (say) a bonnet during certain dancing rituals.If the speaker was aware of this tradition,the saying is quite apt,as this signal is accidental.It might mean that such a person is liable to kill in response to a random event,which would make him more dangerous than someone who will kill at an understood signal.
On the other hand,of course,it could be a meaningless alteration of "drop of a hat",either by mistake or as some kind of mild witticism.People often alter set sayings for the purposes of humour (however slight the humorous effect may be).
__________________能把这段英文解释翻译下吗？拜托了。我给你追加20分。"at the drop of a feather" 可能出自"at the drop of a hat"这个成语at the drop of a hat我知道，是“立即，毫不迟疑”的意思。不错，就是这个意思！