A man has attacked three women in five days, sexually assaulting two, Scotland Yard said.
The screams of all three women caused the attacker to flee after he approached them from behind and covered their mouths.
Two of the victims - who were all in their 20s - were told to keep quiet before being sexually assaulted. The third victim ran away and was not sexually assaulted.
The first two assaults happened in the early evening of Wednesday October 19 in Finchley, north London.
The attempted assault occurred on Sunday October 23 just before 11pm, also in Finchley.
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 can call police on 0208 733 5032 or Crimestoppers on 0800 555 111.