1. Law enforcement officers descended on a high school in Parkland, Fla., where a shooting near dismissal time left at least 17 people dead.

“Oh my God! Oh my God!” one student yelled over and over in a video circulating on social media, as more than 40 gunshots boomed in the background.

A suspect, Nikolas Cruz, 19, who previously attended the school before he was expelled, was arrested about an hour after fleeing the scene, the authorities said.