Death squad is basically a group whose primary activity is extrajudicial killings, basically they are a local mercenary group. The notable example is the Cracha Preto from Max Payne 3.

To the question itself, I was wondering whether there are death squads before the 20th century like antiquity, medieval and early modern period. Most of the examples I saw are usually in the 20th century. I am just curious whether they exist in the form of militia.