Police patrolling a south London estate with mayor Sadiq Khan found a knife hidden in bushes.
London's mayor was shown the site in Tulse Hill where a 17-year-old boy was left fighting for his life after being shot in last week.
Mr Khan said people needed to help be the "eyes and ears" of police to help tackle crime.
It helped because they found a knife today - good example of good policing, finding a knife. It reassures those in the estate. We need the public to realise that they are the eyes and ears of the police - the police are on our side.
The police are the last resort agency who get involved. We're the people who have to go out there and arrest the bad people and most importantly save lives. But knife crime is a complex issue that the police are dealing with in partnership with our stakeholders and people from the local community.
Sadiq Khan said he also understood the concerns of former Oasis singer Liam Gallagher who said the knife crime in London 'freaked him out'.
I take on fully what Liam Gallagher said about his concerns as a dad. We need support from people like him to lobby the government. I want help from parents across London - not just Liam Gallagher - parents across London, if you're a concerned teacher or faith leader or a journalist and you agree with me that the cuts made by central government have gone too far. We want the next Prime Minister to reverse those cuts. Work with me to lobby the governent.