A Good Samaritan was repeatedly punched before being thrown off a train after waking a man up because he thought he would miss his stop.
The 38-year-old victim woke his alleged attacker at St Albans believing he may be about to miss his stop.
But police said the man reacted angrily, causing the kindly stranger to switch carriages.
As the train pulled into Luton Airport Parkway the attacker found the victim and began violently assaulting him, according to detectives.
Police today released CCTV images of a man wanted in connection with the incident on the train in the early hours of Wednesday, 17 June.
The victim was taken to hospital and treated for injuries including a broken and cut nose, swelling to the head and bruising. The alleged attacker left the train at Bedford, police said.
Sergeant Stephen Bartlett said: “This was a violent and sustained assault and we are doing all we can to catch the person responsible. Everyone has the right to travel on the rail network, at any time of day or night, without the fear of violence of any kind.”
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference E/B3 of 26/06/2015. Information can also be passed anonymously to the independent charity, Crimestoppers, on 0800 555 111.
