Detectives are hunting a man suspected of grabbing a string of women in the street after a 24-year-old was sexually assaulted after leaving a Tube station.
Police in Acton, west London, are warning women to be vigilant, especially when walking home from Underground stations and using their phones or wearing headphones.
They have asked anyone who has been victim of a similar assault but not reported it to come forward.
The 24-year-old woman had just left East Acton station between 10.25pm and 10.40pm on March 9 when a man sneaked up behind her and assaulted her.
Police have released a CCTV image of the suspect, who is white or Asian, aged between 20 and 32, 6ft and slim with dark hair. He was wearing a dark-coloured parka with a fur-trimmed hood and shoes with light-coloured soles.
Investigators now believe the same man may have grabbed three other women since the beginning of the year.
The first was an 18-year-old who was listening to music with headphones as she walked along St Andrew's Road in Acton on January 3.
A man grabbed her from behind and reached around to her chest, but she struggled and he ran off.
In another attack a 27-year-old woman who was talking on her phone as she walked from East Acton Tube station on January 25 was grabbed and assaulted.
A 38-year-old woman was also grabbed as she walked along Trinity Way on February 4. The suspect made suggestive comments before running off.
Detective Inspector Ash Hornsby, who is leading the investigation, said: "It is essential we identify and speak to the man in the CCTV image. I would ask the public to look carefully at the image and, if anyone recognises the male, or has any information as to who he is or where he can be found, to contact us immediately.
"I would also urge anyone who was in any of these locations on the days and times of these offences and who may have seen any assault or anything suspicious to get in touch.
"Equally, if anyone has been the victim of an as yet unreported assault then they are urged to contact police."
Anyone with information can call police on 0207 161 9702 or Crimestoppers anonymously on 0800 555 111.