You can refer to a violent person or criminal as a thug .
例句
...the cowardly thugs who mug old people.抢劫老人的胆小恶棍
英汉词典释义
n.
暴徒;恶棍;流氓
He edged away from the thug.他悄悄地躲开了那个暴徒。You have to be tough with these young thugs.对这些青年暴徒态度一定要强硬。The thugs beat him senseless with a baseball bat.暴徒用棒球棒把他打得失去了知觉。The thugs showed no pity.那些恶棍一点慈悲心也没有。A bunch of thugs broke in and smashed the place up.一帮恶棍闯进来把这个地方砸了个乱七八糟。He tried to beat the thugs off with a stick.他想用棍子打走那些流氓。He was beaten up by a gang of thugs.他让一伙儿流氓给打了。