Cyber specialists from a Jewish community nonprofit combing the internet’s deep web were the first to detect a sinister plot to open fire on a New York City synagogue, authorities said Monday. Mitchell Silber, executive director of the UJA Federation of New York’s Community Security Initiative, said it was his group’s discovery of worrisome tweets that sparked the investigation by the NYPD and FBI. Advertisement “There’s a lot of chatter on the internet,” Silber said at a City Hall news conference where he was joined by Mayor Adams and NYPD Commissioner Keechant Sewell. “One of the most difficult things is...