A man was attacked after he asked two boys to stop threatening passengers.
He was assaulted on the train and as he left Harpenden station on April 5.
Two boys boarded a train at West Hampstead Thameslink at 8.20pm that evening and began threatening people.
A fellow passenger challenged the boys' behaviour and asked them to stop.
The two boys became aggressive and started to assault the passenger. When he left the train, he was assaulted further and the boys tried to steal his rucksack. He did not sustain any serious injuries.
The train stopped at all stations between West Hampstead Thameslink and Harpenden.
British Transport Police (BTP) officers are keen to speak to anyone who may have been on the train and witnessed what happened or saw what happened at Harpenden station.
Officers have released CCTV images of two boys as they may have information that could assist the investigation.
You can contact BTP by calling 0800405040 quoting reference 656 of April 5 2018.
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