1.本句的主干是the man killed a man.所以,本句的谓语动词是killed.
2.come from 和the man从逻辑关系上看,的确是主谓关系,come from Beijing在句中作定语修饰the man,由于和它的逻辑主语是主动关系,所以动词ing形式,如果是被动关系,则用动词ed形式,如The man called Jim killed a man.