A 27-year-old man has been charged with first-degree murder over the killing of a nine-year-old boy earlier this month, Chicago police say.
Tyshawn Lee was lured into an alley in the city’s South Side and shot dead because of his father’s gang ties, officers said at the time.
The killing caused outrage in a city with high levels of gun violence.
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.
Separately on Friday, about 2,000 protesters marched in cold wet weather down one of Chicago’s busiest shopping streets to protest over the October 2014 death of Laquan McDonald.
The planned demonstration – which coincided with the busy “Black Friday” shopping day in the US – followed the release of video footage showing police officer Jason Van Dyke shooting the teenager 16 times.
Mr Van Dyke, 37, was charged with first-degree murder on Tuesday.