Police were called to Uxbridge Road in Hanwell, just after noon on Thursday to reports of a woman seriously injured outside the L’Oro di Napoli Italian restaurant.
The woman, named locally as Lilia Djairine, 24, was pronounced dead at the scene after efforts by passers-by to save her failed.
A 28-year-old man who was arrested on suspicion of murder has now been released, police said.
Scotland Yard revealed a post-mortem examination held at Fulham mortuary on Friday found that the cause of death was hanging.
The force said there was no evidence the woman was stabbed.
Inquiries are continuing and anyone with information is urged to call 101 and quote CAD 3314/19July, or Crimestoppers anonymously on 0800 555 111.