Officers are releasing a CCTV image following an assault on a train between Liverpool Lime Street and Lea Green Railway Stations.
On Thursday 30 March, on the 9.51pm service to Manchester Victoria, a 57-year-old man was assaulted by a stranger.
The victim sustained bruising to his face and a fractured cheekbone.
The offender left the train at Lea Green Railway Station.
Officers believe the man in the CCTV may have information that could help their investigation.
Anyone with information or who knows the man is asked to contact BTP by calling 0800 40 50 40 or by texting 61016 with reference 2300036476.
Information can also be given anonymously to the independent charity Crimestoppers on 0800 555 111