"Anyone who recognises the man in the CCTV, or has any other information, is asked to contact British Transport Police by texting 61016 or by calling 0800 40 50 40 quoting reference 742 of 5 February.
Officers now wish to speak to the man in the CCTV images, who "may have information" that could aid their investigation.
British Transport Police said: "Detectives investigating a sexual assault on board a train from Nottingham to Leeds are today releasing these images in connection.
COPS have released CCTV of a man they wish to speak to after a woman was sexually assaulted on a train.
"At about 6:15pm on 5 February a woman was on board a train when a man sat next to her and sexually assaulted her.
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