Nikolas Cruz was apprehended on Wednesday and taken into custody after the shooting.
He has been officially charged with the killings, according to the Broward County Sheriff's Office.
Cruz was a former student and was expelled from the school for disciplinary reasons.
The incident happened at Marjory Stoneman Douglas High School in Parkland, a town about 50km north of Fort Lauderdale, shortly before 3pm as the school day was coming to a close.
The shooting, which claimed 17 lives, left both students and teachers dead and another 15 have been injured.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)