Slain NYPD officer Wenjian Liu is to be sent to Cypress Hills Cemetery in Brooklyn on Sunday. Lu Huiquan / For China Daily

More than 20,000 police officers and civilians turned out Sunday for the funeral of Wenjian Liu, the New York Police Department officer killed in the line of duty last month.

The funeral at the Aievoli Funeral Home in Brooklyn started at 11 a.m. as uniformed police officers from across the United States formed a sea of dark blue on a gray, rainy day, filling several avenues along 65th Street.

Liu's family members recalled details of his life and described him as caring, hard-working and committed to family.

"Wenjian, you are the best son," said his father, Wei Tang Liu. "You are the best husband. Also, you are our police officer and our best friend." The elder Liu described losing his only child as "the most difficult time" and was unable to continue his speech after breaking up.

"To me, he is a soul mate," said Liu's widow Pei Xia Chen, while weeping. "Wenjian is an incredible husband, son, co-worker and friend, my best friend." The couple had been married only since September.

"I do not know why there is so much evil and heartache in our world," said FBI Director James Comey, representing the US government. "Our obligation is to try to make something good out of tragedy, so the evil is not allowed to hold the field, so the evil is not allowed to win the day."

Liu is believed to be the first Chinese-American police officer killed on the job, according to The New York Times. He will be buried in Cypress Hills Cemetery in Brooklyn.

Liu, 32, and his colleague Rafael Ramos, 40, were shot dead in their patrol car on Dec 20 in Brooklyn by Ismaaiyl Brinsley, who then shot himself to death in a nearby subway station.

Brinsley had posted on Instragram earlier about his plan to avenge the deaths of Eric Garner on Staten Island and Michael Brown in Ferguson, Missouri, in incidents involving police this summer.

Liu, a Guangdong native, came to the US as a boy to pursue the American Dream with his parents. He decided to join the police force after the 9/11 terrorist attacks in 2001. He joined the NYPD in 2007 after serving as an auxiliary police officer.

"All of our city is heartbroken," said New York City Mayor Bill de Blasio.

At the end of the funeral, Liu's casket, covered with the NYPD flag of blue, green and white, was carried into a hearse as officers saluted and somber bugle music played. Three helicopters flew across the sky shortly afterward. The hearse, guided and followed by dozens of police motorcycles, moved slowly eastward along 65th Street and was watched by thousands of police officers. They stood in formation until the car disappeared from sight, and some were wiping their eyes.

"They are doing a difficult job every day," retired police officer John Magin told China Daily. "It's getting more difficult throughout the country."

Magin said that ordinary people often see police making arrests but do not see the hardships they endure in protecting communities, including "protecting people protesting them".

Magin was referring to a series of nationwide protests triggered by the deaths of Garner and Brown. De Blasio was considered overly sympathetic to the protesters in the eyes of many police officers, and some turned their backs to the mayor during both funerals.

Both the mayor and the police should "make sure that they go forward together", said US Representative Peter King of New York. "The tragedy can be an opportunity to find a way for the mayor to go with the police."

The wake for Liu was held Saturday at the same funeral home on a cold, rainy day. Media were denied access per the Liu family's request, but people who paid respects said Buddhist rituals were performed, with candles, incense and lotus lights. Family members sat in a room receiving condolences.

"This is a really tragic story," New York Governor Andrew Cuomo said after the wake. "This is really pointless. It had nothing to do with them," he said of Liu and Ramos. "They did nothing wrong. ... It was pure and random hatred."

Martin Golden, a former NYPD officer and a state senator said: "We are going to have a hearing at the Senate to see how we can help the police department get the equipment and training they need."

"We are here to support Liu's family and NYPD officers," said Hannu Tarjamo, one of some 20 officers from the Los Angeles Police Department who attended. "When it happens here, it happens to us. It is a loss to us as well and officers across the country."

Residents and businesses around the funeral home also showed their support by hanging blue ribbons outside their homes.

"It is the time when police officers need public support most," said Sharon Li. "We came to the wake to show our support towards the NYPD."

De Blasio attended the viewing Saturday, but did not give a public speech.

Liu migrated to the US with his family from southeast China in 1994.

"We came to the US and then joined the police, with the same dream and career," said Wu Yachang, a retired NYPD detective with more than two decades' service. "When I knew his story, it was just like looking at me 30 years ago."

"It is a very sad loss and pity," said Guan Ziyuan, representative of the Long Zhang Association. "He was protecting us and our communities, and he was doing good deeds."

Donations have poured in since the officers' deaths. The Stephen Siller Tunnel to Towers Foundation, a non-profit organization helping veterans and firefighters, has announced it would pay off the mortgages of both Liu's and Ramos' families. More than $600,000 out of a goal of $800,000 goal had been raised by Jan 2. Chinese communities also have been raising money for the Liu family.

On Dec 31, de Blasio announced that West 6th Street and Ridgewood Avenue in Brooklyn would be renamed "Detective Wenjian Liu Way" and "Detective Rafael Ramos Way", respectively. The blocks are where the two officers' respective homes are based.

Lu Huiquan in New York, Xinhua and the AP contributed to this story.