Sussex Police said it is hoping to trace a member of the public who might have filmed a man with knives.
Police said a man was seen in Preston Circus, Brighton with a knife at 9.08pm on Wednesday, June 13.
Officers quickly arrived on scene but couldn’t find anyone with a knife or a man matching the description.
PC Marcus Knight said: “It was reported there was a woman filming this man on her phone and we are very keen to trace her and see the footage. She is a vital witness and we would really like to speak to her.
“The suspect is described as white, 5’ 10”, slim, black hair wearing a grey and black Adidas tracksuit.
“If you are this witness or you witnessed this incident please get in touch online quoting serial 1514 of 13/06.”