Three persons were killed and four others injured when a bus whose brakes reportedly failed ran amok here on Friday, police said.A city bus of the state-owned Andhra Pradesh State Road Transport Corp (APSRTC) ran ran over motorists on a busy road near Budameru bridge.While two persons -- a 40-year-old woman and a 12-year-old girl who were riding pillion -- died on the spot, another person succumbed to injuries in a hospital. Four others sustained critical injuries.The brakes of the bus apparently failed leading to the horror, a police officer said. The bus came to a halt after hitting a truck.Irate relatives of the victims set fire to the bus. However, the police, with the help of some people, doused the flames.CCTV images of the horrific incident showed the bus hitting motorcycle from behind and running over them. Three bikes and an auto-rickshaw were damaged in the incident.