A man in his 80s was assaulted and had a large amount of cash taken from his wallet after getting off a train shortly before 5pm on Sunday at the Derriaghy Halt in Lisburn.
Police say the man’s phone may also have been stolen from his pocket, whilst on the train.
The victim was left badly shaken.
Following the incident, police arrested a man in his 50s on suspicion of robbery.
Inspector Moore said: “We are appealing for witnesses who were on the 4.10pm train from Great Victoria Street station in Belfast to Derriaghy, or in the vicinity of Derriaghy Halt around 4.25pm. Did you notice anything suspicious on the train, or upon exiting the train?
“We are keen to speak to anyone who saw two men travelling on the train together, one was described as wearing a pink tracksuit with short hair and in his 30s.
“If you were either on the train or in the station between the above times and witnessed an incident or saw any suspicious activity, contact police on 101 quoting reference number 1566 14/08/22.”
You can make a report online using the non-emergency reporting form via http://www.psni.police.uk/makeareport/ . You can also contact Crimestoppers anonymously on 0800 555 111 or online at http://crimestoppers-uk.org/.