A mentally unstable man snatched a seven-month old toddler from his mother onboard the Delhi-Farakka Express and threw him out of the running train near the Gosainganj railway station here.
Following the incident on Wednesday, passengers thrashed the man and handed him over to the police.
A search was launched to locate the toddler but he was not found.
Government Railway Police (GRP) in-charge, Ayodhya, Subedar Yadav said: "The accused, Kamlesh of Samastipur (Bihar) is mentally unstable. The complainant, Uma Burman, hails from Dakshin Dinajpur in West Bengal."
According to sources, the accused offered to calm the child who was crying and before anyone could realize what was happening, he walked towards the door and flung the toddler out of the train.