Chicago on edge after another arrest
Chicago remained on edge on Monday as a student was charged for threatening to kill 16 white students or staff at the University of Chicago.
The threat came days after a video was released of a police officer shooting 17-year-old Laquan McDonald 16 times.
The video sparked days of protests in the city, where tensions were already high after the killing of nine-year-old Tyshawn Lee earlier this month.
A man was charged with first-degree murder over his death on Friday.
Both incidents caused outrage in a city with high levels of gun violence.
Authorities said Jabari Dean, 21, of Chicago, posted online from a phone that he would "execute approximately... 16 white male students and or staff, which is the same number of time (sic) McDonald was killed" and "will die killing any number of white policemen that I can in the process".
University authorities said a decision to close the campus was taken following "recent tragic events" at other colleges nationwide.
Officer Jason Van Dyke, 37, was charged with first-degree murder last week over the October 2014 death of Laquan McDonald.
Amid protests in the city over Mr McDonald's killing, Corey Morgan, 27, was arrested for killing Tyshwan Lee.
The boy was shot dead because of his father's gang ties, officers said at the time.
The police force in Chicago have vowed to destroy the gang they say was behind the boy's death.
A second suspect is in custody and a warrant has been issued for a third. Chicago Police Superintendent Garry McCarthy said all three suspects had belonged to the same gang.
Police said the death could be attributed to two gangs fighting and retaliating against one another for months.
The arrest came as thousands protested in the city over the 2014 killing of a black teenager by a white policeman.
'Abhorrent and cowardly'
Tyshawn Lee was killed when members of a rival gang lured him away from a park near his grandmother's home and shot him, investigators said.
The man charged is Corey Morgan, a Chicago native, police said.
Mr McCarthy described the shooting as the "most abhorrent, cowardly, unfathomable crime" he had ever seen.
"They're going to be obliterated," he told reporters. "That gang just signed its own death warrant."
Speaking at the boy's funeral, Reverend Michael Pfleger, a local priest and activist, told mourners the killing marked "a new low for Chicago".
Chicago saw 406 murders last year, down from the previous year's total but still higher than other US cities with larger populations, such as New York and Los Angeles.
However, there were also more than 2,500 shootings in the city, up almost 15% on the previous year.