Detective Inspector Craig Bradley said:
"I am appealing for any people who were in the area and witnessed this incident, or the events leading up to this incident, to come forward and speak to my team.
"At this early stage it is unclear what the motive for this incident was.
"If you saw anything, or have any information which may help the investigation, please get in contact."
More top news
Police have identified a man and woman found stabbed to death in Fulham.
The Polish Cultural Association say they are "horrified" following abusive graffiti that was posted on their building in Hammersmith.
A time-lapse video has revealed how Ai Weiwei’s artwork Forever was taken apart.