There didn't seem to be anything unusual about the chilly April night to the two teenage black boys waiting for the bus. It was about 10.30, dance steps were being practised, home beckoned. One of the two walked a little further on the better to see any approaching bus. His friend called out to him asking if one could be seen. Perhaps the sound carried; from the other side of the road, a group of white youths approached, "What, what nigger?" one of them shouted. One of the boys, reflexes sharp, ran but the other found himself "literally engulfed" by the youths. He was stabbed twice. The gang swiftly melted away, the wounded teenager managed to run some 130 yards but soon fell and died. The whole incident must have taken no more than two minutes.
The murder of Stephen Lawrence some 20 years ago and his family's subsequent long fight for justice became one of those emblematic moments in British history, a point at which middle-class complacency about racist attacks and police corruption was shaken. The two decades between that April night and now have seen a failed private prosecution of the murderers, a ground-breaking public inquiry led by Lord Macpherson which controversially found that the Met Police was institutionally racist and at last, a year ago the successful prosecution of two of the group of white youths for murder.
"It was a partial victory," Duwayne Brooks, the friend who was with Stephen Lawrence that night tells me in measured tones. He can still remember Stephen, the boy who was into athletics, "we were always in competition", he says with a smile, his personality and attitude to life. And of course he can remember that April night. "That day is like a freeze frame in everybody's life."
He sensed danger from the white boys crossing the road, "It's that streetwise instinct," he explains. "A survival thing, something is going to kick off in a minute. Do I want to be here or do I want to run?"
The freeze-framed images of that night, the memory of the sense of danger from the approaching white youths in an area known to have problems with racism had the effect of stretching out an incident which took place in minutes into a period which seemed like hours.
"The worst thing was waiting for the ambulance, it seemed like we were waiting forever," Brooks recalls. He speaks coolly, with the voice of someone who has experienced much and reflected carefully upon it. Naturally inclined to the logical, the rational rather than the emotional, he found that the murder accentuated his mind's natural tendency to the precise and analytical.
In the years following Stephen Lawrence's murder, Brooks found himself repeatedly arrested, on one occasion even charged with attempted rape - the charge was thrown out by a judge before it reached a jury - and claimed he was being harassed by the Met.
Still, when we meet, Brooks is keen not to dwell on the past. "That was a period in history," he says. "It was my belief that the Met was out to get me, it might not have been the case but it was my interpretation."
Someone who has been witnessed and experienced all that Brooks has done would be forgiven for sinking into a life of cynicism but instead Brooks is carving out a career in politics. He's now a Liberal Democrat councillor and wants to stand for the Mayoralty of Lewisham next year. His number one priority: tackling gang culture. If he is elected mayor he wants to address gang members himself - "we know who they all are," he declares - and put before them a starkly simple choice either to get behind him and his plan for improving the borough and their lives through mentoring, or continue in crime and as he puts it "see the worst side of my authority".
From the vantage point of professional politics he says he feels Britain has changed since his friend Stephen Lawrence was murdered. "Different parts of the country have changed at different speeds. In London we've seen we are probably the most diverse city in Europe. It wasn't like that 20 years ago."
When it comes to the specific issue of how and to what extent policing has improved in the last 20 years, his thoughts are balanced, considered. He starts with the positive side of the balance sheet: "There are some parts which have improved significantly, community engagement, around the Independent Advisory Groups, family liaison officers, the way victims are looked after and treated, first aid, every officer has first aid training every year. That wasn't happening before."
Then he pauses to consider where policing still falls short: "If we put that to one side and look at police culture, the culture that's in the Met, has that changed, no. Is racism is still endemic in that culture, yes but that doesn't mean that every single officer in the police force is racist but racism is endemic in the culture."
He notes also that too many LGBT police officers still feel constrained to hide their sexuality from their colleagues. "Why in 2013 do officers from the LGBT community, if they are lesbian have to pretend they're going home to their boyfriends, or if they're gay have to pretend they're going home to their wives?" he asks rhetorically.
Just as concerning for Brooks is the matter of police corruption, a persistent thread which ran through the Lawrence murder police investigations. He emphasises that it wasn't Lawrence's murder which caused corruption in south-east London but rather that the murder occurred in a district with a pre-existing police corruption problem. He answers my question about whether he thinks police corruption is still a problem with an emphatic "of course," adding, "We've seen that with the News of the World stuff."
Then he turns to the practicalities: "But how do you weed officers out who've got everybody else by the balls? Is corruption endemic? We don't know. Do police officers go to court and lie on a daily basis. Yes. Is it being monitored? No. If it's not being monitored can we then tackle it? I don't know."
Brooks doesn't claim to know how to untangle the complexity of police corruption but he is clear that a key element must be external monitoring. Similarly, he points to the Macpherson Report and notes that while its recommendations are well known, there is no monitoring of their implementation, no Macpherson Working Group to assess progress in meeting the report's recommendations.
One of the last unfinished tasks he cites of the Stephen Lawrence investigation is an endearingly personal one. Brooks wants those who worked to bring his friend's killers to justice to be given recognition. In particular, he cites the senior investigating officer, Clive Driscoll, who he thinks should have received a commendation from the Met for his work. "This man has had to put up with me for the last few years berating him about the failure of the Met and he always promised me, 'I may not get all of them but I will get some of them', and he fulfilled his promise."