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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 after a gunman killed two New York City officers.

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

The gunman, Ismaaiyl Brinsley, had vowed online to put "wings on pigs" as retaliation for the slayings of black men at the hands of white police.

Police say Brinsley had at least 19 arrests in Georgia and Ohio

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