A knifeman terrorised passengers on a late-night train as he chased eight teenagers through the carriages while brandishing a blade.
Officers were today appealing for help tracking down a man they believe has information about the incident.
It happened on a Liverpool Street to Southend train in the early hours of August 15, British Transport Police said.
The man and teenagers were travelling between Wickford and Hockley at about 1.50am.
Pc Lauren Newling said: “A man on the train got involved in an altercation with a group of teenage boys.
“A fight broke out and other passengers stepped in to stop the violence.
“The older man got off the train, but the two parties continued to argue and the man got back on.
“He produced a knife and chased the teenagers through the train, before leaving at Hockley station.
“Officers now want to speak to anyone who witnessed the incident or has information about what took place.”
Pc Newling said “Thankfully this sort of incident is rare, and in this case nobody was seriously injured.
“However, this was a violent incident which frightened other passengers.
“I think the man in the image we are issuing today has information which could prove particularly useful to our investigation.
“Please let us know who he is.”
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference ESUB/B3 of October 12. You can also call Crimestoppers anonymously on 0800 555 111.
