JERSEY CITY — Friends came to mourn the boy who made good, the one who was robbed on the streets of this city as a teenager and decided he would try to keep them safe for others. Colleagues from near and far came to pay respects to a fellow police officer, a 23-year-old rookie who was gunned down while on duty. And strangers came to send a message that they were tired of the violence.

Hundreds of people gathered inside St. Aloysius Church on West Side Avenue on Friday to remember the life of Officer Melvin Santiago, many still shocked by the callous nature of the crime that left the young officer dead.

The shooting on Sunday, six blocks from where the funeral took place, exposed an undercurrent of tension here, where shiny, new glass towers dot the east side of town, testament to the city’s rapid growth in recent years, while the west side continues to be mired in poverty and crime.

Officer Santiago was the first Jersey City police officer killed in the line of duty since 2009, and his death was a heavy blow for the close-knit police force.