Three women in five days have been attacked by the same man in Finchley, north London, police say.
Two of the victims – who have all been in their 20s – were sexually assaulted.
The screams of all three women caused the attacker to flee after he approached them from behind and covered their mouths.
The first two assaults happened in the early evening on October 19.
The attempted assault occurred on October 23 just before 11pm.
Acting Detective Inspector Warren Kennard said: “Despite these attacks taking place on side streets around Finchley Central and West Finchley Underground stations, we understand that there may be a number of potential eyewitnesses.
“If you were one of them, it’s possible that you may not have realised the nature of the assaults in the belief that they were some kind of dispute, which did not need public or police intervention.
“The reality is that three women have gone through a frightening experience, and I urge anyone who may have seen or heard anything suspicious to come forward and speak to us.”
The suspect is described as having a tanned complexion, likely to be either dark-skinned European/Arabic or light-skinned Asian in appearance. He is in his mid-30s, 5ft 8in to 6ft, of slim build and smelled of cigarette smoke.
He is described as wearing blue jeans with black formal-type shoes.
Anyone with information should call police in Barnet on 0208 733 5032 or Crimestoppers on 0800 555 111.