Given the following passage

"In the American Old West, policing was often of very poor quality.[citation needed] The Army often provided some policing alongside poorly resourced sheriffs and temporarily organized posses.[citation needed] Public organizations were supplemented by private contractors, notably the Pinkerton National Detective Agency, which was hired by individuals, businessmen, local governments and the federal government. At its height, the Pinkerton Agency's numbers exceeded those of the United States Army.[citation needed]",

answer the following question. Note that the answer is present within the text.

Question: What is a group of men formed to find criminals?
posses
The passage states that the army provided some policing, and that poorly resourced sheriffs were supplemented by temporarily organized posses. A posse is a group of men formed to find criminals or other law-breaking individuals in order to bring them back for trial.
So the answer is "posses"..