Thousands of angry students, parents, teachers and neighbors of a Florida high school where 17 people were killed demanded Saturday that immediate action be taken on gun-control legislation, insisting they would not relent until their demands were met.

The rallies in Fort Lauderdale and St. Petersburg gave a political outlet to the growing feelings of rage and mourning sparked by the carnage. Authorities say a former student who had been expelled, had mental health issues and been reported to law enforcement, used a legally purchased semiautomatic rifle to kill students and staff at Marjory Stoneman Douglas High School in Parkland.