NEW ORLEANS — A second suspect has been arrested in the 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.Police suspect the brothers were involved in a neighborhood gang and “engaged in a criminal lifestyle by choice,” Serpas said.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.”In addition to 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.At Thursday’s court appearance, Akein Scott, shackled and wearing an orange prison jumpsuit, stood silently as his court-appointed attorney handled the proceedings.Prosecutors said a witness picked out a photo of Akein Scott, 19, from a lineup. An arrest affidavit said the unidentified witness told investigators that Akein Scott was the person seen in a surveillance video that police released to the public as they searched for him for three days. The witness also said Akein Scott was carrying a silver and black semi-automatic handgun at the shooting scene, according to the affidavit.