New York City Mayor Bill de Blasio and police commissioner Bill Bratton were saluted by police guards as they arrived for the wake of New York Police Department officer Wenjian Liu on a snowy Saturday afternoon in Brooklyn, Reuters reported. Bratton urged police officers Friday to show respect after dozens turned their backs when de Blasio spoke last week at the funeral of Liu’s slain partner, Rafael Ramos.

"A hero's funeral is about grieving, not grievance," Bratton wrote in a memo read at police roll calls during the weekend. "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.”

Liu, 32, and Ramos, 40, were shot to death by Ismaaiyl Brinsley while eating lunch in their patrol car in Brooklyn Dec. 20 amid nationwide protests against the treatment of black civilians by white law enforcement. Brinsley, who committed suicide after the ambush-style attack, had said he would avenge the deaths of Michael Brown and Eric Garner, two unarmed black men who died during the summer at the hands of white police officers. Since the deaths of Liu and Ramos, New York City police have investigated at least 70 threats made against officers and more than a dozen people have been arrested, the Associated Press reported.

A few hundred people, mostly officers dressed in blue uniforms, lined up outside the Aievoli Funeral Home in the Bensonhurst section of Brooklyn Saturday afternoon, waiting for the doors to open and the service to begin, Reuters said. More than 25,000 officers from around the country attended the funeral for Ramos in Queens last weekend, CNN reported. Dozens of officers turned their backs when de Blasio began his eulogy -- a political statement against the mayor for allegedly fueling anti-NYPD sentiments in the city. Bratton described the behavior in his memo as an “act of disrespect," adding, "All the officers were painted by it."

Several NYPD officers have blamed de Blasio for the deaths of Ramos and Liu. “Mayor de Blasio, the blood of these two officers is clearly on your hands,” the New York Daily News quoted Ed Mullins, president of the Sergeants Benevolent Association, as saying last weekend. “It is your failed policies and actions that enabled this tragedy to occur. I only hope and pray that more of these ambushes and executions do not happen again.”

Liu, who is believed to be the first Chinese-American NYPD officer killed in the line of duty, will be buried Sunday at Cypress Hills Cemetery, following Chinese and traditional ceremonies, Reuters said.