One person was killed and two injured on Monday when Sitamarhi police opened fire in its efforts to control a violent mob which was protesting against the killing of a businessman on Sunday night.The incident took place at around 10.30 am when Rajiv Kumar Mishra, 20, an onlooker, was hit fatally by police bullets. The two injured have been admitted to the Sadar hospital and one of them has been identified as Laxman Shah, 19.The mob was protesting against the murder of trader Anil Kumar, 35, by unidentified gunmen at the National Market under Town Police Station under Sitamarhi town.Bihar Chief Minister Nitish Kumar has ordered a police inquiry into the incident by the Divisional Commissioner and Tirhut Range Deputy Inspector General of Police. “I have also sent the Additional General of Police concerned to the spot,” Kumar told reporters.The police said they had to open fire after about 100 protestors entered the Town Police Station premises and torched a police jeep and burnt some documents. Earlier, the mob pelted stones at the police station.Tirhut Range Deputy IGP Arvind Pandey said, "It is too early to say if Mishra fell to police bullets or was killed by some anti-social elements in the mob. An inquiry will clear the air soon," he said.