You can refer to a person who attacks someone as their attacker .
例句
There were signs that she struggled with her attacker before she was repeatedly stabbed.有迹象表明，在她被连刺数刀前，曾与袭击者进行过搏斗。
英汉词典释义
n.
攻击者,进攻者；抨击者
Police are scaling down the search for the attacker.警方正在缩小对攻击者的搜寻规模。He killed the attacker in self-defence.他出于自卫而杀死了袭击他的人。She identified him as her attacker.她认出他就是那个攻击她的人。