A 21-year-old Chicago man has been charged with posting an online threat to kill 16 white people at a University of Chicago campus.
Jabari R Dean is accused of transmitting a threat in interstate commerce, according to a federal criminal complaint.
Dean allegedly admitted to FBI agents that he made the post and took it down shortly afterwards.
All classes were cancelled on Monday at the college because of the warning.
Officials say Dean appears to have been motivated by the 2014 death of a black teenager who was shot 16 times by a white Chicago police officer.
The University of Illinois at Chicago said the person in custody was one of its students living off campus.
Chancellor Michael Amiridis said in a statement: “We are monitoring this situation closely.”
The threat, which was passed on by the FBI, mentioned the Chicago University quadrangle and specified 10am on Monday.
But with a heavy police presence on campus, that time passed without incident.
According to the Chicago Tribune, the FBI were notified on Sunday of a post on the World Star Hip Hop website.
The commenter – who used the initials JRD and a Chicago Bulls logo – said the attack would be in revenge for last year’s killing of Laquan McDonald.
Bail for Jason Van Dyke, 37, who is charged with first-degree murder in the 17-year-old’s death, was set on Monday at $1.5m (£1m).
“This is my only warning,” said the post, according to a police report seen by the Tribune.
“At 10am Monday morning, I’m going to the campus quad of the University of Chicago.
“I will be armed with an M-4 carbine and two desert eagles, all fully loaded. I will execute approximately 16 white male students and or staff, which is the same number of time McDonald was killed.
“I will then die killing any number of white policeman in the process. This is not a joke. I am to do my part and rid the world of white devils. I expect you do the same.”
The college had told faculty, students and non-essential staff to stay away from the Hyde Park campus on the city’s south side on Monday.
Students in college housing were warned to stay indoors.