Jason Downs is a civil rights attorney who has represented the families of Freddie Gray and Terrence Sterling in civil matters arising from their deaths.

Brutality and lawlessness flourish in an environment that condones violence. We must take a long, hard look at the environment that fostered a police officer's failing to activate his body camera and killing an unarmed man by shooting him in the back and neck.

On Sept. 11, 2016, D.C. police officer Brian Trainer shot and killed Terrence Sterling in our nation's capital. Sterling, an unarmed, 31-year-old black man, was shot once in the neck and once in the back. Almost a year went by with only silence from the criminal-justice system. On Aug. 9, the U.S. Attorney's Office announced that it had chosen not to seek an indictment against Trainer on any charges related to the killing.

Immediately after news broke that there would be no charges, Police Chief Peter Newsham and Mayor Muriel E. Bowser (D) asked Trainer to resign. These requests are a step in the right direction. Resignation would be partial justice for the Sterling family, whose lives are forever changed.

But Trainer is not the only problem; there is a culture of violence infecting the D.C. police.

Gangs are known to display colors and symbols to intimidate those outside the gang. Too many D.C. police officers are mimicking these intimidation tactics.

Attorneys with Law for Black Lives DC have uncovered disturbing photographs showing some D.C. police officers displaying logos with a clear message of death. The photos included one of an on-duty officer of the 7th District wearing a T-shirt with a picture of a hooded Grim Reaper holding a rifle and an MPD badge. The T-shirt also subtly depicts a Celtic cross, which has been used by white nationalists, including Norwegian Nazis in World War II.

Does the D.C. police department want its officers to have a gang-like mentality that manifests in the form of symbols of intimidation, hate and acts of violence? The difference between a street gang and these officers is that our criminal-­justice system routinely punishes street gang members. But officers display these violent symbols, and the killing of unarmed citizens apparently goes without consequence.

This attitude of invincibility is to be expected given the District's track record when dealing with police killings. According to the 2016 report, "The Durability of Police Reform: The Metropolitan Police Department and Use of Force," released by the Office of the D.C. Auditor, no D.C. police officer has been charged in connection with a fatal shooting in the line of duty.

In Sterling's case, the U.S. Attorney's Office for the District closed the investigation before the grand jurors voted on whether charges should be filed, saying there was "insufficient evidence." This prosecutorial decision took power away from D.C. residents to decide whether Trainer should be held accountable in a criminal court of law. Equally as concerning, this decision by prosecutors sent a clear message to police officers: The criminal-justice system condones a police officer shooting an unarmed man.

Trust between the community and the police is disappearing. To even begin to develop trust, our leaders must show a commitment to systemic change, including of the culture within the D.C. police department. Asking Trainer to resign was the first step. The next step is acknowledging the culture condoning violence within the department. Step three would be ridding the department of any police officer who creates, wears or glorifies messages of hate and violence.