A man sexually assaulted a teenage girl on a London tube train before horrified passengers stepped in.
Police have released CCTV images of a man they would like to speak with following the attack on a Northern Line service between Stockwell and South Wimbledon.
A man made sexual remarks to a teenage girl at around 11.15pm on Wednesday, February 19.
He then sat next to her and sexually assaulted her.
Other passengers intervened and the man left the service at South Wimbledon.
Officers believe the man in the CCTV images may have information that could help their investigation.
A spokesperson for the British Transport Police said: 'Anyone who recognises the man in the CCTV, or has any other information, is asked to contact British Transport Police by texting 61016.