该杀人犯显然精神失常。The murderer was apparently mentally disturbed.无人理会杀人犯的求饶.The murderer's entreaties for mercy availed to nothing.那个杀人犯完全是丧心病狂.The murderer was completely unbalanced....

“杀人犯”的英语可以翻译为：[法] manslayer，[电影]Murdere...