翻译：这个年轻人成为杀人凶手的原因是什么

what is the reason for (promotes/generates) this young man to be a murderer?

这个年轻人成为杀人凶手的原因是什么
--What cause the youngest became a man-killer?.

what is the reason that young guy becomes a murderer?

what is the reason for that young guy to commit such a murder?

what makes the young man a murderer ?