US police departments warn officers to wear bullet-proof vests when out on patrol

US police departments and union leaders 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 and shot them to death inside their patrol car.

The killing of Officers Rafael Ramos and Wenjian Liu on Saturday afternoon in Brooklyn heightened fears about the safety of law enforcement officials, but authorities haven’t said if they believe any threats are imminent.

The gunman, 28-year-old Ismaaiyl Brinsley, had vowed in an Instagram post to put “wings on pigs” as retaliation for the slayings of black men at the hands of white police. Brinsley was black; the slain New York Police Department officers were Hispanic and Asian.

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.

The slayings come at a tense time as police nationwide are being criticised following Garner’s death in a New York officer’s chokehold and Brown’s fatal shooting in Ferguson, Missouri. Protests erupted in recent weeks after grand juries declined to charge the officers involved.

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.”

The president of the detectives’ union told members in a letter to work in threes when out on the street, wear bulletproof vests and keep aware of their surroundings.

Meanwhile, New York Mayor Bill de Blasio faces the biggest crisis of his political career. New York police officers turned their backs on de Blasio in protest during a news conference and their union said the mayor had blood on his hands after Saturday’s shooting.

De Blasio, elected last year on a promise to advance civil rights after two decades of tough policing helped New York shed its reputation for violent crime, was sympathetic to the protesters who poured into New York’s streets after a grand jury declined earlier this month to indict the officer who killed Garner in a chokehold in July as he resisted arrest.