On Sunday at the funeral for Liu, it appeared fewer officers turned their backs as Mayor Bill de Blasio spoke than during the service for Ramos.
Some officers have accused the mayor of encouraging anti-police fervor because of his support of protests against police brutality. Tens of thousands had taken to the streets after the death of African-American Eric Garner during an encounter with white NYPD officers in July.
Pat Lynch, head of the Patrolmen's Benevolent Association, has taken aim at de Blasio, even saying the mayor's office was stained with the two dead officers' blood.
But before Sunday's funeral, Bratton urged officers to be reverent.
"A hero's funeral is about grieving, not grievance," Bratton said in a memo. He said the earlier display put all NYPD officers in a bad light.
"It stole the valor, honor and attention that rightfully belonged to the memory of detective Rafael Ramos's life and sacrifice," his memo read.
On Saturday, there was no protest by the police against the mayor. Several officers saluted de Blasio when he arrived for Liu's wake.
The best of what the U.S. can be
At the Sunday service, the slain New York Police officer was remembered as a family man, a dedicated police officer, an avid fisherman and a person who embraced the best of what the United States can be.
Liu was 12 when his parents emigrated with him in 1994 from Canton, China.
His family said that the first souvenir he bought when he arrived was a sticker of the Statue of Liberty. He valued law and order and always wanted to be an officer.
Weeping, his wife Pei Xia Chen told the thousands of mourners who gathered at Brooklyn's Aievoli Funeral Home that her husband was dedicated to his job and he understood the awesome responsibility it entailed.
"We spoke about work often," she said, "and how much respect he had for the law, how he applied the law ... with courtesy, with respect and with the highest professionalism."
The couple had been married for only two months when Liu was shot to death December 20 as he sat in his patrol car next his partner, Officer Rafael Ramos. In uniform, Ramos and Liu were apparently murdered simply because they were cops. Their killer had posted on social media his desire to end police officers' lives.
In the immediate aftermath of the slayings, de Blasio called the attack on the officers an attack on all New Yorkers.
On Sunday, the mayor said that Liu, as well as Ramos, "embodied our city's most cherished values."
"(In their deaths, we lost) the very best of us. ... We lost two individuals who were showing us the way," the mayor told mourners.
Ramos saw his work as ministry and was posthumously appointed honorary NYPD chaplain
. He was just hours away from becoming a lay chaplain and graduating from a community-crisis chaplaincy program before his death. He left behind a wife, Maritza, and two sons, Justin and Jaden.
Though he majored in accounting in college, Liu joined the police force where he served for seven years. He used his Chinese-language skills as whenever he could, his family said.
Bratton described him as an especially empathetic person who often listened to the people he served in New York. Being a cop is about more than paperwork and arrests and keeping watch, Bratton said, it's also about being kind.
"For seven years, he sought out" those who were suffering and tried to ease that.
At Ramos' funeral last weekend, Bratton promoted both men to the rank of detective, first grade.
Officer Liu "believed in the possibility ... of a city free of fear," Bratton said, and is the type of "officer that we want ... and the type that we have."
De Blasio praised Liu for his love of family. The officer rarely took time off but when he did, Liu went fishing. And in those wonderful moments when he caught a big fish, he would share it with his parents and his wife.
He was a "brave and skilled police officer but he was also a kind man, a kind officer, someone who gave of himself," the mayor said. "He wanted to help others in everything he did."
Liu "walked a path of courage, path of sacrifice, a path of kindness," the mayor continued. "This city welcomed Detective Liu. New York stands a little taller today because of the time he walked among us."
FBI director James Comey was the first to address mourners, speaking about what drives officers to do their job despite the risks. "They want to do good ... they want to make ordinary life" better," he said.
Though political and law enforcement leaders gave moving comments, hearing from Liu's family members was truly heartbreaking.
Liu's father wept as he praised his son in Cantonese, saying he was grateful for how much Liu cared for him.
Pei Xie Chen spoke directly to her husband: "You were an amazing man."
Diversity and unity
The ceremonial burning of paper money and the melodic sounds of Buddhist chants marked Liu's wake Saturday.
There were throngs of police officers -- many who had traveled from across the country to pay respects in New York. They represented many different cultural backgrounds, like Ramos and Liu.
Ramos, a New York native of Puerto Rican descent, was remembered last week at a massive gathering at a Protestant church in Queens.
"This was his dream, to become an NYPD officer," New York Gov. Andrew Cuomo said outside Liu's wake Saturday. "In some ways, it's the ultimate assimilation into America, into New York, to become a police officer. And obviously he was so proud, and he was so proud for his whole family."
Cuomo was unable to attend Sunday's service due the recent death of his father.
After Liu's funeral, Lynch of the Patrolmen's Benevolent Association told reporters that some officers "feel like they were turned upon by City Hall and we have a right to express our opinions as well, and they did respectfully."
Officers who turned their backs when the mayor spoke did not act, Lynch said, "inside a church, not inside the service, but outside where it should be done, on the streets, like we have a right to do."
"This was an organic gesture that started on the streets of New York, and it should be respected," he said.
After Sunday's service, a drum corps played as officers walked block after block as Liu's body was transported from the funeral home. Officers from around the country joined local officers paying tribute.
For more than a half mile away in any direction from the procession, one could see a huge wall of police uniforms.