Ania Jedrkowiak, a Polish national, was found with stab wounds in an alleyway off Church Gardens, South Ealing, shortly after midnight on Tuesday and was was pronounced dead at the scene despite the efforts of emergency services.
A 29-year-old man was arrested on suspicion of murder and has been taken into custody.
Detectives say the arrest is “significant” and that the victim and suspect were known to each other.
A 20-year-old man had also been arrested on suspicion of murder but was released with no further action.
Officers are speaking with Ania’s next of kin, and are being supported by specialist officers.
Detective Chief Inspector Brian Howie, who is leading the investigation, said: “We have now made a second arrest, which we believe is a very significant one in this investigation. The victim and suspect were known to each other.
“We are examining CCTV and speaking to any witnesses who have come forward. However, we are always keen to hear from anyone else who has not yet spoken to us but who thinks they may have seen or heard anything, no matter how small, that could help.
“In particular we would urge anyone who lives or was travelling in the area of South Ealing Road, between 11.15pm on Monday, May 16 and 1am the next day, or anyone who has CCTV or a doorbell camera, or a dashcam, to check it for anything that appears out of the ordinary.”
Church Gardens, South Ealing Google Maps
Officers had attended along with London Ambulance Service and London’s Air Ambulance.
Chief Superintendent Sean Wilson, who is in charge of policing for west London, including Ealing, said: “This is a tragic incident that I know has come as a shock to the local community.
“Officers remain at the scene as our searches and forensic examinations continue. We will also have additional visible patrols in the local area tonight and in the coming days.
“We are grateful to those who live and work nearby for their support and understanding as we continue our work. We recognise the inconvenience it has caused.
“Where possible we have taken steps to allow businesses and other venues such as the local church to reopen as soon as our investigation allowed.
“I am particularly mindful of the proximity of this incident to a local school – something which meant the school had to remain closed on Tuesday.”