Mayor Bill de Blasio has faced a firestorm of criticism from New York police in the wake of the shooting of Wenjian Liu, 32, and his partner Rafael Ramos on December 20.
Hundreds of police officers pointedly turned their backs in a protest against de Blasio during a funeral for Ramos last week, prompting Bratton to press his force to avoid a repeat of those scenes at Liu's funeral today.
<divid='ndtvrelcontent'></div>De Blasio made a low-key appearance at a wake held for Liu in Brooklyn, leaving shortly after his arrival without speaking to reporters. Journalists were not given access to the wake.
Images of de Blasio entering the Aievoli Funeral Home appeared to show officers saluting as the New York mayor passed up steps into the building.
Liu and Ramos were shot dead by a gunman who claimed to be acting in revenge for the deaths of unarmed black men at the hands of police.
Thousands are expected to turn out for Liu's funeral today, with high-level guests to include de Blasio and FBI Director James Comey.
Call for 'decency'
Bratton has previously decried the snub that greeted de Blasio as he addressed mourners at Ramos's funeral as "very inappropriate."
"A hero's funeral is about grieving, not grievance," Bratton wrote in a memo to the 34,000 New York police officers.
"I issue no mandates, and I make no threats of discipline, but I remind you that when you don the uniform of this department, you are bound by the tradition, honor and decency that go with it."
Bratton said the protest at Ramos's funeral "stole the valor, honor and attention that rightfully belonged to the memory of detective Rafael Ramos's life and sacrifice."
"That was not the intent, I know," Bratton added. "But it was the result."
More than 20,000 police officers from across the United States attended the funeral for Ramos.
Liu and Ramos, 40, were shot in the head as they sat in their patrol car by Ismaaiyl Brinsley, who police said had a clear anti-police bias and posted anti-government comments on Instagram that referenced two unarmed black men killed recently by police.
The killing of the two officers in broad daylight shocked New Yorkers and caused a long-running dispute between the mayor and the police to spill over into public view.
Some officers have been highly critical of de Blasio for remarks about police relations with black Americans that they say incited the shooting.
They remain angered, in particular, over de Blasio's statement that he counsels his biracial son to be particularly careful around police officers.