He campaigned on a promise of restoring "law and order", winning the endorsement of America's largest police union, the Fraternal Order of Police.
We went into the process thinking the code of silence was just this unwritten agreement among police officers to protect one another. And what we found was that the contract itself institutionalises these private understandings among police officers that make it harder to identify and root out bad behaviour.
Now, as US President-elect Donald Trump prepares to take office, Fault Lines travels to Chicago to look at how a contract between the city and the Fraternal Order of Police gives police officers special privileges when they are being investigated in a shooting.
In the first 24 hours after a police-involved shooting, investigators are not allowed to question police.
Union officials describe it as a "cooling-off" period, but critics say it's created a culture of impunity, giving officers time to manipulate the facts.
There's no better example of this than the case of Laquan McDonald, who was shot and killed by police in 2014.
Officers allegedly intimidated witnesses, destroyed evidence, and filed false police reports claiming the teenager attacked them. But video of the incident told a different story: McDonald walking away as police officer Jason Van Dyke opened fire and shot him 16 times.
A mayoral-appointed task force which studied the union contract says it also makes it harder for police whistleblowers to report misconduct, and also mandates that police disciplinary records be destroyed after five years.
Fault Lines reporter Sharif Abdel Kouddous investigates whether a labour agreement between the City of Chicago and the Fraternal Order of Police is standing in the way of justice, transparency and accountability.
Source: Al Jazeera