 Security on heightened alert as millions gather to celebrate the 4th of July. ABC's Aaron Katursky. Intelligence bulletins obtained by ABC News detailed serious concerns not only about the New York fireworks, but about Independence Day celebrations in San Francisco and in Las Vegas. And a leading concern is that some lone offender is going to turn to violence without warning. But there's no indication of an organized plot. And as the mayor here says, the whole city is going to be enjoying 4th of July.