A 51-year-old man was assaulted on a train close to Newry train station.
The train was travelling between Dublin and Belfast on September 6 when the incident occurred.
And police in Craigavon are asking people who may have been on the train at the time for information following the assault.
Constable Adam Khattak said: “Around 8.30pm on Sunday, 6 September, a 51 year old man was assaulted on a train travelling from Dublin to Belfast.
“The assault occurred close to Newry Train Station and the man sustained injuries to his face.
“We would like to hear from anyone who witnessed this assault or has information in relation to this incident. We can be contacted in Lurgan on 101, quoting ref: 1070 060915.”
If you prefer to provide information without giving your details you can contact the independent Crimestoppers charity anonymously on 0800 555 111.