Police are offering £20,000 to anyone who has footage of a fatal knife attack that happened in Peckham Rye.
Bilal Kargbo, 26, was stabbed to death in Blenheim Grove, on April 28, and detectives believe someone may have caught the incident on their smartphone.
The Metropolitan Police said a crowd of up to 70 people were at the scene and some of them were filming.
Mr Kargbo was killed in broad daylight at around 3.15pm and died close to a phone shop on Rye Lane where he worked.
Detective Inspector Jason Grafham said: ‘Our inquiries have led us to believe that a large crowd gathered around the altercation Bilal was stabbed during – a crowd of around 60 to 70 people.
‘Crucial to our investigation, the inquiry team believe a number of people recorded the attack on their mobile devices.
‘Therefore we are now offering a reward of up to £20,000 for video footage that would assist and ultimately lead to the conviction of the person or persons responsible.’
Relatives of Mr Kargbo, a father-of-three from south London, added: ‘Please think of the trauma and hurt caused to our family.
‘Our family is absolutely devastated with Bilal’s loss; he was a wonderful father, partner, son and friend.
‘Bilal meant so much to us and it is heart-breaking to know that we will never see or speak to him again.
‘It is hard to put into words the suffering that this has caused our family and it will take a long time for us to come to terms with what has happened.’
Anyone with information is asked to call police on 020 8785 8267 or Crimestoppers anonymously on 0800 555 111.