A second suspect was arrested in the New Orleans shooting that injured 20 people at a parade on Mother's Day, police said Thursday afternoon.

Shawn Scott, 24, was arrested Thursday, police Chief Ronal Serpas said. He is the brother of 19-year-old Akein Scott, who was arrested Wednesday night in the shooting.

Both face 20 counts of attempted second-degree murder, and Serpas said investigators believe the Scotts worked together in the shooting.

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

At a news conference at the shooting site near the French Quarter, Mayor Mitch Landrieu accused the suspects of "callously shooting into crowds of hundreds of citizens."

"The culture of violence is unnatural and unacceptable," Landrieu said, calling the shooting site "holy ground."

Besides the Scotts, Serpas said police arrested four people who are accused of helping Akein Scott elude capture. Serpas said their charges are being accessories after the fact to attempted second-degree murder and obstruction of justice. They range in age from 19 to 32, he said.

The mass shooting showed how far the city has to go to shake a persistent culture of violence that belies New Orleans' festive image.