You can refer to a violent person or criminal as a thug .
例句
...the cowardly thugs who mug old people.搶劫老人的膽小惡棍
英漢詞典釋義
n.
暴徒;惡棍;流氓
He edged away from the thug.他悄悄地躲開了那個暴徒。You have to be tough with these young thugs.對這些青年暴徒態度一定要強硬。The thugs beat him senseless with a baseball bat.暴徒用棒球棒把他打得失去了知覺。The thugs showed no pity.那些惡棍一點慈悲心也沒有。A bunch of thugs broke in and smashed the place up.一幫惡棍闖進來把這個地方砸了個亂七八糟。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.他讓一伙兒流氓給打了。