Who kills her is still a mystery. ?

问题描述:

Who kills her is still a mystery. ?
我看了几个关联词引导的主语从句,发现凡是who引导的主语从句.在主语从句中,就没有
主语.是这样么,am i right?
麻烦大家在不忙的时候解答下,谢谢

Who kills her is still a mystery.
Who既是主语从句的引导词,又是主语从句当中的主语.它身兼二职.