Monday classes at the University of Chicago were cancelled after the FBI warned officials of an online threat of gun violence.
Students and staff are being encouraged to stay away from the school's main campus of the city's South Side, and students who live on campus are being urged to stay indoors. The University of Chicago Laboratory Schools, the libraries and other campus facilities will also be closed.
On Monday afternoon, a spokesman for the U.S. attorney's office in Chicago confirmed someone had been arrested in connection to the threat but said charges are pending. The University of Illinois at Chicago said that one of its students who lives off-campus had been arrested.
On Sunday, University President Robert Zimmer sent out an email explaining that FBI counterterrorism officials had told staff "that an unknown individual posted an online threat of gun violence against the University of Chicago, specifically mentioning 'the campus quad' on Monday morning at 10 a.m."
The email continued: "Based on the FBI's assessment of this threat and recent tragic events at other campuses across the country, we have decided in consultation with federal and local law enforcement officials to exercise caution by canceling all classes and activities on the Hyde Park campus through midnight on Monday."
The university's medical center will remain open to patients but there will be further security measures, according to the statement.
"I'm not going down there tomorrow, and I don't have plans on going down there on Tuesday," one student told the Chicago Tribune. "For a threat like this, I want to give a few days to cool off. I think it's pretty extraordinary that the president interceded and canceled everything. I think that suggests something pretty serious is happening."
FBI investigators are trying to identify the person behind the threat and continue to investigate.
Classes are expected to resume on Tuesday.