TOM HAYS, Associated Press

NEW YORK (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 after a gunman ambushed and 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 (IHSH’-mayl) Brinsley, had vowed online to put “wings on pigs” as retaliation for the slayings of black men at the hands of white police.

Investigators are trying to determine if Brinsley had participated in any protests over the deaths of Michael Brown and Eric Garner or simply latched onto the cause for the final act in a violent rampage.