Under gloomy skies on a chilly Sunday morning, police officers from around the nation packed the streets of Dyker Heights for the funeral of NYPD Det. Wenjian Liu -- who was killed protecting the city he loved.

His was a classic New York story.

Immigrating with his family from China in the early 1990s, Liu came to the city seeking a new life of hope and responsibility. He found it in the NYPD. Like most cops, he took seriously his mandate to keep the city safe and hold society together. And because of that commitment, he and Det. Rafael Ramos lost their lives late last month in an assassination on a street in Bedford-Stuyvesant.

There is no way in the world to redeem an act so tragic, so stupid, so horrific.

The only way forward, as Mayor Bill de Blasio said Sunday, is to focus on the spirit of decency and duty that Liu and Ramos embodied and use those values to tighten the common bonds that exist between the NYPD and the city's 8.4 million residents. This shouldn't be impossible.

More binds us together than keeps us apart.

We all want safety and respect. De Blasio worries about what might happen if his biracial son, Dante, ever got stopped by the police. Liu's father says he worried daily that his son would come home from work safely.

Yet a dangerous gap persists.

Minority communities complain bitterly about racial profiling and lack of respect. They point to the death of Eric Garner at police hands on Staten Island as evidence.

Patrol cops say they're unfairly seen as an occupying army in some districts. In truth, the NYPD's 22,000-member patrol force -- 53% black, Latino and Asian -- looks more than ever like the city itself.

Meanwhile, many cops see the mayor as an ideological enemy. Some turned their backs to him again Sunday.

Garner died because he was black, protesters say. Liu and Ramos died because they "were blue," Police Commissioner William Bratton says. Both complaints are deeply disturbing. Both beg for an honest solution. So far, we haven't seen one.