According to the military regulation that rule Judea and Samaria, when someone (even a civilian) witnesses an individual committing property crimes or about to commit property crimes, they have the authority to detain that person for three hours while the magav/police are called. These latter officials then have the authority to arrest. The army knows full well they can detain Israeli citizens for the police - they do it every day to the Left.
Mexico: Death toll 27 after truck hits religious procession (AP)
from the article: Israel must enforce law on West Bank settlers