Detectives are renewing appeals for information following a linked series of sexual assaults in the Cricklewood area.
Officers believe that 17 incidents, committed between February and December 2018, where lone women have been approached and sexually assaulted by a man, are linked.
Detective Sergeant Neal Heffernan, of the North-West Command Unit, said: "We have carried out extensive enquiries into these sexual assaults, and have made a number of arrests as we attempt to establish what has taken place.
"I would continue to urge anyone with information to call police. It is also possible that there are further victims who, as yet, have not reported the crimes. I would encourage them to come forward and speak with us.
"As the festive season continues we would recommend that people plan their journeys in advance and report anyone they believe to be acting suspiciously.
"We have also increased patrols in the area; these officers will be happy to speak with anyone and offer crime prevention advice and reassurance."
The offences have predominately occurred over the weekend, in the late to early hours of the morning.
In the majority of the offences, the suspect has approached the women as they are walking in the street from Willesden Green Underground Station and attempted to engage them in conversation, asking for a kiss or hug, before touching them.
The suspect has been described as a black man, of medium build who is aged in his 20 to 30s and wearing dark clothing.
Anyone with information is asked to contact Brent CID on 07747 476161 or via 101. Alternatively, call Crimestoppers anonymously on 0800 555 111.
Crime prevention advice and methods to stay safe are available from our website
As part of the ongoing investigation four people have been arrested on suspicion of sexual assault.
A 37-year-old man [A] was arrested on Thursday, 19 July and released under investigation.
A 32-year-old man [B] was arrested on Saturday, 13 October and later released with no further action.
A 34-year-old man [C] was arrested on Sunday, 14 October and released with no further action.
A 24-year-old man [D] was arrested on Sunday, 9 December. He was bailed pending further investigation.