The Railway Protection force on Thursday sacked the RPF constable Chetan Singh, who shot dead his senior and three passengers on board a moving train last month. According to the sources, the orders for his dismissal has been issued by Railway Protection Force (RPF) senior divisional security commissioner on Monday.The officials informed that before this also, Singh was found caught in at least three discipline-related incidents.Notably, Singh has been accused of gunning down his senior officer, Tikaram Meena, and three passengers when the Jaipur-Mumbai Central Superfast Express was near Palghar station on the outskirts of Mumbai in the early hours of July 31.The deceased passengers were identified as, Abdul Kadar Mohamed Hussain Bhanpurawala, Sayyad Saifuddin and Asgar Abbas Shaikh. All of them were travelling in different coaches of the train. However, soon after the horrific incident, the RPF constable Singh was arrested by the Government Railway Police (GRP).According to GRP, the accused first fired RPF Assistant Sub-Inspector Meena then a passenger in B5 coach with his automatic service weapon. The second passenger in pantry car and third was shot dead in S6 coach.However, the motive behind the incident is not clear and the constable is still under probe.