The deceased has been identified as Junaid (17) while his brothers Hasim (21) and and Sakir (23) were injured, Deputy Suprintendent of Police (DSP), Faridabad Government Railway Police (GRP), Mohinder Singh told PTI.
"Sakir is serious," the DSP said, adding that the GRP has registered a case of murder.
Singh said the incident happened last night on board the Delhi-Mathura passenger train between Ballabgarh and Mathura stations.
He said a passenger used a knife to stab one of the brothers to death.
"The passengers thrashed the three brothers badly and attacked them with a knife," he said.
No arrests have been made so far, the officer said.