NEW YORK (CBSNewYork/AP) — Big-city police departments and union leaders around the country are warning the rank and file to wear bulletproof vests and avoid making inflammatory posts on social media in the days after a man ambushed two officers in Brooklyn and shot them to death inside their patrol car.

The slayings of Officers Rafael Ramos and Wenjian Liu Saturday afternoon in Brooklyn heightened fears about the safety of law enforcement officials nationwide, though there is no evidence any threats are imminent.

The gunman, 28-year-old Ismaaiyl Brinsley, had vowed in an Instagram post: “I’m putting wings on pigs today. They take 1 of ours, let’s take 2 of theirs.”

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Investigators are trying to determine if Brinsley had taken part in any protests over the deaths of Michael Brown and Eric Garner, whose names he invoked in his online threat, or simply latched onto the cause for the final act in a violent rampage.

As CBS2’s Jessica Schneider reported, the chaotic murder has prompted beefed up security measures city-wide.

NYPD Officers will stand guard in front of all precincts, they will no longer work alone, conducting all foot patrols in pairs, and auxiliary patrols which involve officers who do not carry weapons have been cancelled.

Lawmakers are also proposing legislation that would outfit patrol cars with bulletproof glass.

After the officers’ killings, a union-generated message at the 35,000-officer NYPD warned officers that they should respond to every radio call with two cars “no matter what the opinion of the patrol supervisor” and not make arrests “unless absolutely necessary.”

Sergeant Benevolent Association President Ed Mullins said officers should double up on calls and stay on high alert.

“My directive to my officers is to go home safe,” he told 1010 WINS. “What’s occurring throughout the city as of yesterday was that lug nuts on private vehicles and department vehicles [were] loosened up on the cars.”

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A memo from an NYPD chief asked officers to limit their comments “via all venues, including social media, to expressions of sorrow and condolence.”

Officials in New York have investigated at least a dozen threats against police since the shootings and one man was arrested at a Manhattan precinct after he walked in and said: “If I punch you in the face, how long would I go to jail?” and refused to leave.

In Memphis, Tennessee, a man was questioned after allegedly posting threats against the NYPD online, CBS affiliate WREG reported.

The alleged threat appeared on an Instagram account hours after Saturday’s shooting, WREG reported. The post said: “Good job. Kill em all I’m on the way to NY now #shootthepolice 2 more going down tomorrow,” according to the station’s report.

“The atmosphere seems to be continuous where threats to police are pretty high and in the end, I think that the officers should be backing each other up,” Mullins said.

Another directive warned officers in Newark not to patrol alone and to avoid people looking for confrontations.

New Jersey State PBA Executive Vice President Marc Kovar said in the email Sunday morning that all members and officers should take extra caution and change up routines in the coming weeks.

He cites heightened hostility from nationwide protests that he says has led to a “fever pitch of anti-police sentiment.”

“This open hostility has created more tense encounters with officers even on routine incidents such as motor vehicle stops,” the alert reads.

In Philadelphia, Police Commissioner Charles Ramsey urged the leaders of protests over the deaths of Garner and Brown to “call for calm and not let this escalate any further.” In Boston, Police Commissioner William Evans said police issued an alert to officers to warn them about the New York City slayings and added that the department had issued several alerts following the decision by the Ferguson grand jury.

At a news conference in New York on Sunday, Chief of Detectives Robert Boyce detailed Brinsley’s long criminal record, hatred for police and the government and apparent history of mental instability that included an attempt to hang himself a year ago.

Brinsley had at least 19 arrests in Georgia and Ohio, spent two years in prison for gun possession and had a troubled childhood so violent that his mother was afraid of him, police said. He ranted online about authority figures and expressed “self-despair and anger at himself and where his life was,” Boyce said.

Hours before shooting the officers, Brinsley had shot and wounded his ex-girlfriend, Shaneka Thompson, at her home in Baltimore. Authorities have said Thompson is expected to survive.

After leaving Baltimore, authorities said, Brinsley took a bus north to New York City and used Thompson’s phone to write the message on Instagram.

Once in New York and shortly before he opened fire on the officers, Brinsley walked up to people on the street and asked them to follow him on Instagram, then told them, “Watch what I’m going to do,” Boyce said. Then he approached the squad car and fired four shots, killing the policemen. He ran into the subway station and committed suicide.

At the site of the shooting Sunday, a makeshift memorial with an NYPD baseball cap, flowers, teddy bears and candles lay in remembrance of the officers.

Ramos’ 13-year-old son, Jaden, said in a Facebook post that Saturday was the worst day of his life.

“Today I had to say bye to my father,” Jaden wrote. “He was the best father I could ask for. It’s horrible that someone gets shot dead just for being a police officer. Everyone says they hate cops but they are the people that they call for help.”

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