At around 11.20pm on November 14, a fight broke out between two men and two women on board the Tonbridge to Gillingham service.
One of the men was placed in a chokehold, and the other man was hit over the head with a bottle, causing a fracture to his nose.
Today (November 29), officers have released images of people who they believe may have information which could help the investigation.
Anybody who recognises any of the people pictured or has any information should contact BTP by texting 61016 or calling 0800 40 50 40, quoting reference 853 of 14 November.
Alternatively, call Crimestoppers anonymously on 0800 555 111.
