Women have been warned not to use headphones or mobile phones while walking alone after a series of sex assaults near a Tube station.
Ten separate assaults on lone women in Cricklewood are thought to be linked, police said.
Most of the attacks have taken place near Willesden Green Tube station, where the latest victim was assaulted early on Sunday.
The Met urged women to "take care" when walking alone.
Sunday's attack, on Walm Lane, happened when a woman was approached by a man who attempted to engage her in conversation before sexually assaulting her.
Officers believe the offence is linked to nine separate incidents between February and September.
In most of the cases, lone women were attacked at weekends by a man attempting to engage them in conversation by asking for a kiss or a hug.
Describing the assaults as "shocking", Det Const Laura Avery, of the Metropolitan Police, said: "I would appeal to women in the local area to take care when they are walking, especially if they are alone.
"Always stick to well-lit streets. If possible, let someone know when you are coming home and the route you are taking and always be alert in your surroundings, so don't use earphones or handheld devices.
"If you see anything suspicious, contact police immediately."
The suspect is described as a black man, of medium build, aged in his 20-30s and wearing dark clothing.
A 37-year-old man arrested on 19 July on suspicion of sexual assault has been released under investigation.