A woman was sexually assaulted on board an Elizabeth Line train just after 7pm on February 7.
British Transport Police said that a man boarded a train at Custom House station and sat down next to the victim.
It is alleged that he then sexually assaulted her before following her off the train at Whitechapel station.
He then followed her through the station and onto a London Overground train.
CCTV images have now been released of a man police wish to speak to as they believe he may have information that could assist with the investigation.
Anyone who recognises him is asked to contact British Transport Police by texting 61016 or by calling 0800 40 50 40, quoting reference 191 of 5 February.
Alternatively, you can contact Crimestoppers anonymously on 0800 555 111.
