Head Constable Ajai Pal Singh and Constables Ahmad Ali, Ram Naresh and Om Singh, who were on escort duty, had been suspended, the officer said.
On Monday night, some 12 armed persons entered a bogie of the Allahabad-Meerut Sangam Express after it stopped between Bharthana-Ekdil railway stations, GRP Station Officer Yashpal Singh had said.
They shot at and injured three medical students who challenged them.
The miscreants looted cash, mobiles and ornaments before fleeing after pulling the chain.