Two passengers were injured after a stone was thrown into the Dhaka-bound Joyantika Express near Tongi station on the evening of 2 August.
Arman Mia said he and his younger brother Fahim Mia had boarded the train at Ashuganj and were seated in coach 'Ta' when the stone came through a window.
He said the stone first hit another passenger in the head and then struck Fahim, 14, in the neck.
Liton Mia, 50, said he boarded at Mukundapur station and that he was hit in the head before the stone injured Fahim.
Liton said he expected to undergo a CT scan in Dhaka.
Railway police constable A. Rauf said passengers are instructed to keep windows closed after trains depart, though some leave them open because of the heat.
Rauf said arrangements would be made for the two passengers to receive initial treatment.
The evidence provided does not identify who threw the stone or state whether any investigation or arrest followed.