Two persons, including the Station House Officer of a police station were killed and another injured when a mob protesting the death of two persons in a road mishap clashed with the police in Vaishali district.Additional Director General of Police (Law and Order) Alok Raj said the clash erupted after locals expressing their ire on the crushing to death of an elderly person and his grand-daughter by a speeding pick-up van yesterday, torched four houses, including that of the driver.The pick-up van, over which the driver had lost control, after crushing to death the two had even ploughed into their house at Agarpur and damaged it.When police rushed to the spot today, the mob pelted stones on them and the station house officer of Patedhi Belsar police station, Ajit Kumar sustained serious injuries.Kumar was rushed to Patna Medical College and Hospital (PMCH) here and he succumbed to his injuries during treatment, Raj said.He said as the situation threatened to go out of control, the policemen opened fire and two youngsters - one 17 years old and another 12 years were injured.They too were rushed to PMCH where the elder of the two died during treatment, Raj said.The ADGP (Law and Order) and local senior civil and police officials are camping in the village to monitor the situation which is tense but under control.Raj said additional police and RAF personnel have been deployed in the village and a flag march was conducted to ensure peace in the village.The driver of the pick up van has been arrested for rash driving, he added.