Killing people for no reason is an example of a barbarous act.
Inappropriate, barbarous behavior.
A barbarous punishment; a barbarous tyrant.
I did but prompt the age to quit their cloggs.
By the known rules of antient libertie,
When strait a barbarous noise environs me.
Of Owles and Cuckoes, Asses, Apes and Doggs - I did but prompt the age to quit their cloggs, John Milton (1673)