Detectives have released an image of a man whose help could be "vital" in an assault on a woman as she travelled on a train.
British Transport Police (BTP) are investigating the attack, which happened on board a service travelling between Newcastle and Chester-le-Street.
They believe he may have "witnessed the assault or have information which may prove vital."
During the journey on Saurday, April 6, a man threw coins at a woman following a verbal altercation on board the 10.22pm service from Newcastle.
A BTP spokesman said: "At Chester-le-Street the man threw another coin, which provoked the woman to challenge his behaviour.
"The man then proceeded to kick the woman harshly in the chest, causing her to fall from the train and onto the platform.
"She sustained bruising to her chest, elbow and hip.
"Officers believe the man shown in this CCTV image may have information which could help them investigate. "
If you know who he is, please contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting reference 1900029454. Or you can call Crimestoppers anonymously on 0800 555 111.