Three persons were killed and one injured in an incident of firing by unknown people near Salem motorway interchange in Sargodha on Monday. According to Police sources, the unknown armed men opened indiscriminate firing on a car resulting in the death of three persons on the spot. Another one in the car was seriously injured who was rushed to nearby hospital. On receipt of information of the incident, police party reached the spot. Police sources said the firing incident was due to old enmity between two parties.