MUMBAI: The Anti Terrorist Squad (ATS) of Mumbai Police interrogated the Railway Protection Force (RPF) constable, Chetan Singh, accused of killing four people, including a 57-year-old assistant sub-inspector (ASI), onboard Jaipur-Mumbai Express train, officials said on Thursday.

According to officials, Chetan, who is presently in the custody of the Mumbai Government Railway Police (GRP), was grilled for questioning by the ATS for hours.

The accused RPF constable Chetan Singh allegedly shot dead Assistant Sub-Inspector Tikaram Meena and three passengers on the moving Jaipur–Mumbai Superfast Express near Palghar station in Maharashtra on July 31.

A five-member high-level committee has been constituted to investigate the incident.

The Borivali GRP has recorded the statement of over 20 people. "Police are reaching out to those present on the train at the time of the incident to get a better understanding of the situation. They have requested people to come forward so that the sequence of events can be understood properly," a senior official with GRP said.

Following the incident, an FIR has been registered at Borivali Government Railway Police (GRP) in Mumbai against Singh under sections 302, Arms Act and Railway Police Act and he was arrested.

Earlier, Chief PRO Western Railway, Sumit Thakur said, "In an unfortunate incident in Jaipur-Mumbai Superfast Express, a police constable shot at his colleague escort-in-charge ASI Tika Ram. The reason for this is not established yet. It is regretted that ASI Tika Ram and three other civilians died. Constable was arrested by RPF/Bhayandar. Further investigation is on."

According to a statement by Western Railway, an ex gratia of Rs 10 lakh has been announced for the passengers who died and the family of ASI Tikaram will receive dues as per service rules.