Akein Scott, 19, was arrested yesterday night in the Little Woods section of New Orleans. He was already facing a gun and drug possession charge and was out on bond at the time of Sunday's shooting at a parade through a neighbourhood near the French Quarter.
The mass shooting showed how far the city has to go to shake a persistent culture of violence that belies New Orleans' festive image.
It was not immediately clear why 20 counts were filed when authorities have said 19 people were injured. Police were expected to release more details on the case today.
Courtney Moles, whose apartment overlooks the shooting site, said she didn't feel her safety was in jeopardy while police searched the city.
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"I didn't really think he would come back. It's more personal than that," she said. "He wasn't going to that second line to make national news. He was probably settling some kind of score."
Moles, 24, said the arrest underscores the city's crisis of violence among its young people. "His life is over now, too," she said of Scott.
Officials initially said three people were spotted running away from the shooting scene, but Scott has been the only suspect identified publicly.
Investigators launched an intense search for Scott, with police Superintendent Ronal Serpas urging him to surrender at a news conference Monday and warning the teen that "we know more about you than you think we know." At one point, SWAT team members and US marshals served a search warrant at one location but did not find Scott.
Police offered a USD 10,000 reward in the case, and investigators received several tips after images from the surveillance camera were released.