British Transport Police detectives are appealing for information after a man launched a tirade of racist abuse at an eastern European woman who asked him to stop swearing in a train carriage.
The man was reportedly asked to moderate his language while speaking on the phone during a journey from London's Liverpool Street station to Walton, Essex on 7 December.
However, according to eye witnesses, the woman's intervention only made the man more offensive.
The man, thought to be aged between 20 and 30 years old, began abusing the woman and continued for 20 minutes. When other passengers intervened, the abuser apparently issued intimidating threats against them.
The man is thought to have left the service at Kelvedon.
DC Reed, the investigating officer, continued: "This kind of behaviour is totally unacceptable and we are determined to find the person responsible.
"We would encourage anyone who recognises the man in the picture, or knows his whereabouts to get in touch. I would also like to appeal to anyone who was on the train at the time and witnessed the incident to come forward."
Call British Transport Police on 0800 40 50 40 with information. Alternatively, call Crimestoppers anonymously on 0800 555 111.