Police are calling for witnesses who may have information about a fatal stabbing of a young man in Brent Cross earlier this year.
Police have released CCTV images of four people who left Brent Cross Underground Station and were in the Heathfield Gardens area at the time of the stabbing.
Detective Inspector Shaun Fitzgerald said: "We have spoken with a number of people as part of our ongoing investigation into Joseph's murder.
"However, the two men and two women in the images we have released today are yet to speak with us.
"It is possible that they may believe that they did not witness anything, however any piece of information regardless how minor it may seem, could be important to our inquiry.
"I would urge them to contact the incident room."
The investigation is being handled by the Met's Homicide and Major Crime Command.
A 21-year-old man has been charged with murder in connection with the fatal stabbing.
A 20-year-old was arrested on suspicion of violent disorder and has been bailed to a date in April.
Two more men identified only as "A" and "B" were arrested on suspicion of affray.
"A" has also been bailed to a date in April, while "B" was released with no further action.
Anyone with information is asked to contact the Incident Room number on 020 8358 0100 or Crimestoppers anonymously on 0800 555 111.
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