An Indian railway security officer opened fire on a moving train in the country’s western Maharashtra state on Monday, killing four people, according to a spokesperson for the Western Railway.

The incident occurred on a passenger train traveling from Jaipur to Mumbai around 6 a.m. local time (8:30 p.m. ET Sunday), the spokesperson told Indian news agency Asian News International on camera.

The spokesperson alleged that Railway Protection Force constable Chetan Kumar killed his colleague and three other passengers.

“A constable, Chetan Kumar, opened fire on his colleague Tikaram Meena and during the incident three other passengers were also shot,” the spokesperson said.

He was arrested by police after he pulled the alarm and jumped off the train, the spokesperson continued.

An investigation is underway, the spokesperson said, adding the reason behind the shooting is “yet to established.”

The victims are still being identified based on the passenger list, he added.

Divisional Railway Manager Neeraj Kumar told reporters that the families are being contacted and compensation would be given to the next of kin.