Historically, U.S. Marshals in the West would deputize a posse of men when needed to capture a fugitive or perform other law-enforcement tasks. Today, the U.S. Marshals Service still authorizes special deputations for fugitive apprehension or other federal law enforcement tasks. However, individuals must meet strict requirements before they are eligible for special deputation.
Individuals must be United States citizens and be currently employed with a law-enforcement agency or other agency approved by the Department of Justice to be eligible for special deputation. In addition, applicants must have successfully completed a law-enforcement training program and have at least one year of law-enforcement experience. Finally, applicants must qualify with an approved firearm and be free from any domestic-violence convictions.
http://work.chron.com/marshals-special-deputation-requirements-23923.html
Always have to regulate guys out of the posse.