Two New York police officers were ambushed Saturday by Ismaaiyl Brinsley after he had made threatening posts online, including a vow to put "wings on pigs" and references to high-profile cases of white police officers killing unarmed black men. After shooting the officers, Brinsley ran into a subway station and committed suicide.

The killings of officers Wenjian Liu and Rafael Ramos have raised concerns in the already tense nationwide debate surrounding police conduct. Some key developments since the weekend shooting in New York:

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AMID CALLS FOR RESTRAINT, PROTESTS GO ON

Despite calls from New York's governor, the city's mayor and others calling for restraint, hundreds of protesters marched through midtown Manhattan on Tuesday night, with some holding signs saying "Jail Killer Cops."

The protesters were mostly peaceful as they wound through the city's bustling shopping district.

Mayor Bill de Blasio on Monday called for a pause in protests over police conduct. He faces a widening rift with those in a grieving police force who accuse him of creating a climate of mistrust that contributed to the slayings.

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ON HIGH ALERT

Security was increased at some police stationhouses in New York as authorities investigated threats made since the shootings, and at least four people were arrested over threats.

An 18-year-old who posted a threatening message on his Facebook profile was facing charges of terroristic threats and man who walked into a police precinct and suggested he would punch officers was arrested, authorities said. Two Staten Island residents also were arrested in cases related to threats.

Officials said they had assessed hundreds of online postings and calls to emergency lines, initiating about 40 threat probes, with about half of those being closed or referred to other agencies.

Police did not detail the threats that prompted Emergency Services Unit officers to provide additional protection at two precincts in Brooklyn, where Liu and Ramos were slain.

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TRIBUTES, MEMORIAL VISITS

Landmarks including the Empire State Building and the Rockefeller Center Christmas Tree dimmed their lights from 9 p.m. to 9:05 p.m. Tuesday to honor the slain officers.

The mayor and his wife quietly visited the site of the shooting on Tuesday morning, spending several minutes there.

De Blasio folded his hands before him and stood with his head bowed. His wife placed flowers among dozens of tributes.

Later, de Blasio observed a moment of silence at 2:47 p.m., the time the officers were shot.

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ONE FUNERAL SCHEDULED

A wake for Ramos will be held Friday at Christ Tabernacle Church in Glendale, Bratton said. Ramos' family said he was deeply religious and heavily involved in the church. The funeral will be held there Saturday. Vice President Joe Biden said he plans to attend Ramos' funeral.

Liu's family is traveling to the U.S. from China and will decide on arrangements after it arrives, Bratton said.

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ABOUT THE GUNMAN

Emerging details on Brinsley are clarifying a portrait of him as a mentally disturbed loner.

His mother told the Daily News he'd had psychological problems all his life but his family never had any indication he would attack police. Shakuwra Dabre said her 28-year-old son had made suicide attempts starting when he was 13, had been institutionalized and had been on and off antidepressants for years.

She says he rebuffed his family's pleas to get help and she last spoke to him in July. She told the newspaper she was "deeply sorry" for what he had done.