Morgan Roof entered the school with marijuana, pepper spray, and a knife after posting a message on social media that police say caused panic among students.
The 18-year-old has since been arrested and charged.
No students were harmed by Roof, the sheriff’s department has reportedly said.
In a post on Snapchat, Morgan Roof said she hoped student participating in a national walkout protesting gun violence would “get shot”.
She said: “You’re walking out for the allowed time of 17min, they are letting you do this, nothing is gonna change what the f*** you think it’s gonna do?
“I hope it’s a trap and y’all get shot we know it’s not fixing nothing but black people are walking out anyway.
“No offence of course.”
Dylann Roof murdered nine black parishioners in the hate-fuelled massacre on June 17 three years ago.
He later admitted to carrying out the shooting in an attempt to provoke a race war between whites and blacks in America.
The shooter was sentenced to death in January last year.
More to follow…