Police announced Friday that they had made an arrest in the death of Tyshawn Lee, a 9-year-old whose alleged gang-related slaying spurred outrage in Chicago.

Chicago police detectives made “an arrest in the unspeakable murder,” department spokesman Anthony Guglielmi tweeted early Friday.

Corey Morgan, 27, was arrested and expected to be charged with first-degree murder, KTLA sister station WGN reported.

Police suspect Lee was shot because of his father’s gang ties, Chicago Police Department Superintendent Garry McCarthy told WGN.

“We’re pretty sure that this is not an accident,” McCarthy said, claiming that the boy was targeted because of his “family relationship with a member of a gang.”

Morgan, initially a person of interest in the boy’s death, had been detained and questioned about the shooting.

He was released after posting the required 10 percent of a $1 million bond in connection to a weapons charge issued because he was not allowed to own a firearm due to a previous conviction, WGN reports. Details on the previous conviction were not immediately known.

Morgan was later arrested, police announced Friday, and he was expected to appear in court Monday.

The boy was shot in the face and back on Nov. 2 as he headed to a park down the street from his grandmother’s house to play basketball, the Rev. Michael Pfleger said at the funeral.

He was “lured” into an alley in what McCarthy called “probably the most abhorrent, cowardly, unfathomable crime that I’ve witnessed in 35 years of policing.”

Chicago was called the murder capital of the United States after it registered 503 homicides in 2012, more than any other city.

Those numbers have ticked down, though the FBI’s 2014 statistics showing 411 killings still outpaced other cities (such as New York with 333 and Los Angeles with 260) with higher populations.

The Auburn-Gresham neighborhood, where gangs battle over turf and the right to sell drugs, and where Tyshawn was gunned down, is among the most dangerous.

Even for a city accustomed to gun violence, Tyshawn’s shooting was considered beyond the pale.

Pfleger, a Catholic priest and local faith leader, called it “a new low.”

“A baby was executed,” said Pfleger, an outspoken advocate against gun violence. “A baby was assassinated right behind us in the alley.”

One longtime resident, Deronce Curd, had trouble coming to grips with the idea of gangs going after children.

“How can a little boy, 9 years old, defend himself?” Curd asked. “This is just — I’m speechless to what is going on right now.”