Police say they have arrested a second suspect in the shooting that injured 20 people at a parade on Mother's Day.

Police chief Ronal Serpas identified the second suspect as 24-year-old Shawn Scott, brother of 19-year-old Akein Scott.

Akein Scott was arrested Wednesday night. Serpas says Shawn Scott was arrested Thursday. Both face 20 counts of attempted second-degree murder.

Akein appeared before a magistrate judge Thursday. His bond was set at $10m.

Serpas says four additional people have been arrested and charged with harboring the suspects. Investigators believe the Scotts worked together in the shooting.

Akeint, 19, was arrested 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 neighborhood 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' good-time image.

It was not immediately clear why 20 counts were filed against the pair when authorities have said 19 people were injured. Police were expected to release more details on the case Thursday.

Courtney Moles, whose apartment overlooks the shooting site, said she didn't feel her safety was in jeopardy while police searched the city.

"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 Akein Scott.

Police have not established a motive and haven't said whether they know the identity of the shooter's target. Officials initially said three people were spotted running away from the shooting scene.

Investigators launched an intense search, with police superintendent Ronal Serpas urging Akein Scott him to surrender at a news conference Monday and warning him 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 either suspect.

Police offered a $10,000 reward in the case, and investigators received several tips after images from the surveillance camera were released.

Police also previously said Akein Scott had an arrest record involving drug and weapon charges. Court records show some had been dropped, but he was facing a felony charge of illegally carrying a weapon while in possession of a controlled dangerous substance.

The video released Monday showed a crowd gathered for the parade suddenly scattering in all directions, with some falling to the ground. They appear to be running from a man in a white T-shirt and dark pants who turns and runs out of the picture.

Gun violence has flared at two other city celebrations this year. Five people were wounded in a drive-by shooting in January after a Martin Luther King Jr Day parade, and four were wounded in a shooting after an argument in the French Quarter in the days leading up to Mardi Gras. Two teens were arrested in connection with the MLK Day shootings; three men were arrested and charged in the Mardi Gras shootings.