Police were called at 10.40pm on Tuesday, 4 June to reports of a fight on Bell Street, at the junction with Edgware Road, NW1.
Officers responded and found a man suffering from a knife wound injury.
They administered CPR before London Ambulance Service paramedics arrived.
Sadly, despite the best efforts of emergency services, the man – aged in his late 20s – died at the scene.
Police believe they know who the man is and are working to inform his next of kin.
Three men have been arrested and remain in custody at central London police stations.
A number of crime scenes are in place and urgent enquiries are progressing.
It was reported that at least one gunshot had been fired.
Any witnesses or those with images and video that could help police should call 101 or get in touch with @MetCC ref CAD 8545/04JUN.
To remain 100% anonymous contact the independent charity Crimestoppers on 0800 555 111.
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