“ You’re Fucked .” This prophetic phrase was etched on the ejection port cover of the police-issued AR-15 assault rifle that Officer Philip Brailsford used when he shot and killed an unarmed Daniel Shaver. The inscription is harrowingly similar to the ironically-termed “love notes” written on American bombs meant for enemy forces.

During his trial, Officer Brailsford claimed he reacted according to his training – he thought he was dealing with an armed person. Yet disturbing footage from a police body camera shows Daniel Shaver following police instructions, all but for a second when he reached toward his waistband. Brailsford fired.

No weapon was found on Shaver’s person. Rather, it seems that Shaver was simply trying to keep his basketball shorts on, which had been falling off as he crawled toward police as ordered. Officer Brailsford was later acquitted of any criminal charges.

Sadly, this hasn’t been the only time police militarization has contributed to civilian harm. On Aug. 17, 2014, an eight-year-old boy was hit by police tear gas meant to disperse Ferguson protestors who had gathered after Officer Darren Wilson fatally shot Michael Brown. Following the release of the grand jury decision regarding whether to charge Officer Wilson, St. Louis Police Chief Sam Dotson declared that his force was ready for any public reaction: “We’ve had three months to prepare [. . .] Our intelligence is good. Our tactics are good.” This statement eerily mimics a commander’s rallying war cry before a final attack – not a call for public order and safety during a time of intense emotion and frustration.

Police made a similarly belligerent statement after the shooting of Justin Way. Way’s girlfriend called for nonemergency assistance when Way began threatening to harm himself while holding a knife. Way later ignored police instructions to let go of his knife and was shot. Instead of carefully parsing his words as he spoke to Way’s distraught family, Detective Mike Smith bluntly explained to Way’s mother that her son was shot because “[t]hat’s what we do.”

These accounts demonstrate an important externality of American police militarization: mission creep.

The phrase “To Protect and to Serve” functions as the mission statement of our police departments today. This mantra originated from a 1955 contest to find a motto for the Los Angeles Police Department police academy, and has since grown to include the call “to serve mankind,” “to protect the innocent” and “to respect the Constitutional rights of all men to liberty, equality and justice.” Officers also promise “never [to] emplo[y] unnecessary force or violence.” Communities such as Ferguson, Sacramento and Baton Rouge may beg to differ.

While there is no doubt that the vast majority of police live by this motto, the perception in America – especially among communities of color and the impoverished – is that the mission has changed. The officer’s call to “protect and serve” has, in many cases, slowly and quietly become indistinguishable with the soldier’s call to “ engage and destroy .”

Police weapons were meant to serve as instruments of protection and used for defensive means. However, the M-4s and tanks that police use today are offensive weapons – meant to “ engage and destroy targets in the context of war .” Indeed, “weapon system” is the exact phrase used by the military to describe tools of war.

Police departments themselves have even begun to think of their own roles in militaristic terms. After Justin Way’s fatal shooting, St. Johns County Sheriff’s Office Commander Chuck Mulligan said the use of M-4 assault rifles is warranted in cases such as Way’s “if the deputies feel that that is the appropriate weapon system to use.”

Psychologist Philip Zimbardo’s famous Stanford prison experiment reminds us of the importance of role casting – and warns of its potential dangers. During the experiment, Zimbardo assigned his subjects one of two roles: guard or prisoner. He then sought to determine whether the subjects would be influenced by the expectations of their assigned roles or if they would continue to act according to their own personalities.

Zimbardo quickly found that the former was true. Students soon abandoned their respective personalities and internalized their assigned roles. After a prisoner rebellion, “The guards broke into each cell, stripped the prisoners naked, took the beds out, [and] forced the ringleaders of the prisoner rebellion into solitary confinement, and generally began to harass and intimidate the prisoners.” Prisoners were forced to relieve themselves in buckets placed inside their cells. Guards broke down prisoner alliances by placing a few prisoners in “privilege cells,” giving credence to the belief that these individuals were informants against the rest. A prisoner began showcasing signs of “acute emotional disturbance” less than two days after the experiment began.

Recent research suggests that police are vulnerable to a similar change in personality. A 2017 study demonstrates that the dramatic increase in the amount of military equipment available for use by our local police departments is associated with increased police violence and civilian casualties. This association remained significant even when taking into account other factors such as household income, population, the level of violent crime, drug use and reverse causality (i.e., whether the militarization was a response to violent crime, or vice versa).

How does this affect the police’s duty “to protect the innocent” or “to respect the Constitutional rights of all men to liberty, equality and justice”? This study showcases that police militarization is an impediment to the fulfillment of these sacred duties.

Our police officers should be our local superheroes. Their presence should bring comfort, not instill fear. The militarization of our local police forces works directly against this aim. When police are dressed and armed as if they are ready to conquer enemy combatants, their role becomes unclear – both to them and to the communities they have sworn to protect.

Policing is a profession with significant safety risks. It is understandable that we would want to provide our local superheroes with equipment that we believe would diminish some of this danger. But for the sake of public safety and trust, let’s keep the line between police blue and military green clear.

Arthur Rizer is a DPhil student at the Centre for Criminology. Arthur is also the criminal justice policy director at the R Street Institute, a Washington D.C. based think tank (@arthurrizer).