The Justice Department is updating its use of force policy for the first time in 18 years, saying explicitly that federal officers and agents must step in if they see other officers using excessive force. The policy takes effect on July 19. The new policy is outlined in a memo Attorney General Merrick Garland sent to senior Justice leaders. The rules apply to all agencies under the Justice Department, including the FBI, DEA, ATF and U.S. Marshals Service. "It is the policy of the Department of Justice to value and preserve human life," the policy begins. It later adds, "Officers may use force only when no reasonably effective, safe, and feasible alternative appears to exist and may use only the level of force that a reasonable officer on the scene would use under the same or similar circumstances." The policy's first portion deals with deadly force, barring tactics such as firing guns to disable cars. But the next section calls for de-escalation training, and the next two spell out situations in which officers have an "affirmative duty" " to prevent or stop other officers from using excessive force, and to render or call for medical aid when it's needed. Law enforcement officers should be able to recognize and act on "the affirmative duty to intervene to prevent or stop, as appropriate, any officer from engaging in excessive force or any other use of force that violates the Constitution, other federal laws, or Department policies on the reasonable use of force," the policy states.