Police are continuing to search for two people whose CCTV images they released after a train inspector was stabbed in the back for challenging two youths travelling without tickets.
The incident occurred at East Tilbury station in Essex just before 9pm on Friday on the 8.20pm c2c service from Southend Central to Fenchurch Street in London.
The 42-year-old ticket inspector was stabbed after asking the pair to get off the train, British Transport Police said.
He was taken to Basildon University Hospital where he received three stitches.
Police have issued CCTV pictures which show two suspects, both white and in their late teens, one wearing a black hooded top and the second a grey top and grey flat cap.
Chief Superintendent Paul Brogden, of British Transport Police, said: "This was an appalling and disgraceful attack on a man who was simply doing his job and who had quite rightly asked the men to leave the train."
Julian Drury, managing director of c2c, added: "We deplore this incident which is being fully investigated by the British Transport Police. Thankfully incidents of this nature are extremely rare and maximum efforts are being made to identify the suspects."
Bob Crow, general secretary of the Rail Maritime and Transport union, said: "Once again it shows the dangers that transport staff face every day and particularly over the Christmas and new year period.
"The perpetrators of this vicious and cowardly assault must be caught and the authorities need to show that those who attack public service workers will be severely punished."