The uncle of a murdered Upper Norwood teen told families who have also lost loved ones to gun and knife crime: "We have to give back life. It's easy to become haters".
Mr Jackson was one of dozens of grieving family members to attend a special memorial service in Wandsworth last week.
The event was organised by Mitcham mum Iffat Rizvi - whose daughter Sabina was shot dead in 2003 - to give grieving families a chance to share their experiences.
Addressing the crowd, Mr Jackson described how his family had suffered and been separated by some members having to go into a witness protection programme.
Leroy Jackson's nephew Jordan Lee Jackson, 20, was shot dead along with his girlfriend Leyla Djemal-Northcott, 21, in 2006.
They were slain by two masked gunmen in their Menlo Gardens flat. The two killers have never been brought to justice.
Mr Jackson said: “We will never get over the loss. You learn to live with it. The damage that the loss causes also brings damage between families because each individual grieves differently.
“Every one of us that has lost have felt that loss. We have life to give back. We have to give back life. It’s easy to become haters.”
He advocated better home discipline to stop young people getting involved in guns, knife, and crime.
He added: "The bullet once leaving the gun doesn’t discriminate on who it takes. It has no preference to colour or age or gender.
“There’s not winners, there are only losers. What I don’t want to happen is for our young people who are supposed to be human beings to grow up like beasts in the field. Our upbringing was to behave like decent and responsible young people.”
Speakers from families across London said they were frustrated by the lack of support for grieving families, and called for longer jail terms for murderers.
The mourners were joined by community workers and victim support groups for the memorial.
Mrs Rizvi, who runs the charity Sabina's Trust Against Revolvers and Racism, said the families would meet again soon to campaign for changes to the education and justice systems.
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