A gunman opened fire at a Florida high school on Wednesday afternoon, killing multiple people, officials said. The Broward County Sheriff's Office tweeted that there were "at least 14 victims" after the shooting at Marjory Stoneman Douglas High School in Parkland. It was not immediately clear how many of those victims were injured and how many had died. But Sen. Bill Nelson, D-Fla., citing Broward County officials, told NBC News that there were "a number of fatalities." "This is a really bad day," the senator said.