Multiple attackers killed 12 people and wounded at least nine others in a late-night mass shooting in the South African city of Johannesburg, police said Wednesday.Police believe more than 10 suspects were dropped off in a minibus in an informal settlement in the Cleveland suburb of Johannesburg late Tuesday night and opened fire on people.The victims were nine males and three females, according to police. Eleven of them died at the scene and the 12th died in the hospital.Police are searching for the attackers, and no arrests have been made. The motive for the shootings was not yet clear, they said.Informal settlements in South Africa are unplanned residential areas usually made up of shacks or similar structures.