Anarul Haque (30), a BSF constable of 119 battalion who was sitting inside the bus, was killed on the spot and two others were injured in the accident at Simanagar under Chapra police station, said district SP Sabyasachi Raman Mishra.
Anarul was declared brought dead at Shaktinagar Hospital while two others are being treated there.
The driver and the conductor of the bus ran away, police said adding that irate locals ransacked 12 vehicles and put the killer bus on fire soon after the mishap.