We won't give up until ALL Stephen Lawrence's killers are jailed, say parents Doreen and Neville Lawrence trying to gather strength to mark killing She will attend London memorial, he will take flowers to Jamaica grave Stephen was stabbed to death at bus stop in Eltham, London, in 1993 Last year Gary Dobson and David Norris were jailed for role in murder But three other prime suspects in case still continue to evade justice Keeping on: Doreen Lawrence poses in December 2011 with a picture of her murdered son, Stephen The parents of murdered teenager Stephen Lawrence have vowed never to give up their quest for justice ahead of today's 20th anniversary of his stabbing. Doreen and Neville Lawrence were united in their message as they tried to gather strength to mark his appalling racist killing. Although 4,500 miles apart - one will attend a memorial service in London, the other will take flowers to Stephen's grave in Jamaica - they defiantly insisted they have not given up hope that one day all his killers will face justice. Mrs Lawrence vowed to hold the head of Scotland Yard to account over his recent pledge not to close the investigation, while her former husband said he believes detectives could yet nail all those responsible. In January last year, two of the original five suspects accused by the Daily Mail of murdering Stephen in Eltham, south-east London, in 1993 were convicted of his killing after a forensic breakthrough. Drug trafficker Gary Dobson, 37, and gangster's son David Norris, 36, were jailed for life for their role in the murder. But three of the other prime suspects named by the Mail in its famous front page in February 1997 - brothers Neil and Jamie Acourt and their friend Luke Knight, who all still live in south-east London - continue to evade justice. Senior political figures and Met chief Sir Bernard Hogan-Howe are among the VIPs due at a memorial service for Stephen in London today. David Cameron said last night: "The senseless killing of Stephen Lawrence in 1993 was a tragedy. Killed: Stephen Lawrence, 18, an aspiring architect, was stabbed to death by a group of five or six racist thugs - all white youths - as he waited for a bus in Eltham, south-east London, on 22 April, 1993 'It was also a moment that sparked monumental change in our society - change that has been brought about by the tireless efforts of Stephen's family in challenging the police, Government and society to examine themselves and ask difficult questions. In an article for the Mail, Home Secretary Theresa May says: "Stephen's murder became a catalyst for a drastic, and sometimes agonised, reappraisal of the police's approach to racist crime. Today, it is almost inconceivable that a black woman whose son had been murdered would be treated in the way Doreen Lawrence was in 1993. In an interview with the Mail, Mrs Lawrence, 60, conceded that Scotland Yard's inquiry into her son's murder cannot go on indefinitely but said the time for it to be shelved had not yet arrived. Jailed: In January last year, two of the original five suspects accused by the Daily Mail of murdering Stephen - drug trafficker Gary Dobson (left), 37, and gangster's son David Norris (right), 36, were convicted of his killing Just after the court case last year, there were rumours that certain officers felt that they had gone as far as they could go. Named: Brothers Neil (pictured) and Jamie Acourt and their friend Luke Knight continue to evade justice I think at the time I questioned that. Because I feel that, yes, evidence is now difficult to come by after 20 years and you need that to convict the other three. But I don't think they should give up and the fact that the Metropolitan Police Commissioner is saying that is good. Mr Lawrence, 71, who will say a prayer at his son's grave in Jamaica with a pastor friend who has flown from England, is equally determined that police continue their investigation. "It took us nearly 20 years to get this result [guilty verdicts]," he said. I do not know if I am going to live another 20 years but I have not given up. I think that all those people who told me to give up do not understand the nature of love. Mr Lawrence - who split from Stephen's mother in 1999 - suggested someone might confess or provide vital information. Stephen, 18, an aspiring architect, was stabbed to death by a group of five or six racist thugs - all white youths - as he waited for a bus in Eltham on 22 April, 1993. Last month Dobson dropped his appeal against his conviction, a move seen by Yard chiefs as an admission of guilt. But Mrs Lawrence said she doubts whether he will ever publicly admit his guilt. Looking ahead to today's memorial service, she said: "I have been feeling very low recently. It is difficult to believe it is 20 years since I saw my son, 20 years of speaking out against racism, 20 years of challenging the police, challenging the Government. But one of the things I have always said is that Stephen deserved better. He did not deserve what happened to him. Mrs Lawrence said that, in her opinion, the police are still racist and she accused the Government of not doing enough on the issue of racism. The Stephen Lawrence Charitable Trust is dedicated to providing opportunities for disadvantaged young people and maintaining Stephen's legacy. To support its work, click here. To find out more about the Trust, click here. Fifteen years ago: Neil Acourt is pictured (front) in 1998 at a public inquiry into Stephen Lawrence's death In the 20 years since the ghastly murder of Stephen Lawrence, policing in Britain has been transformed. That is in large part due to the unstinting efforts of Doreen Lawrence, Stephen's mother, who has pushed and pressured the authorities relentlessly and effectively - first to get the Met's initial inquiry into Stephen's murder reviewed, and then to improve the way Britain's police handle and investigate racist killings. Stephen's murder became a catalyst for a drastic, and sometimes agonised, reappraisal of the police's approach to racist crime. The Macpherson Report identified the Met as "institutionally racist," and triggered very significant changes in police practice. The police are more sensitive to race issues than they used to be. The toleration of racist banter that used to be such an offensive and depressing characteristic of many police canteens has diminished. No one who cares about policing in Britain can be complacent. There are no grounds for thinking everything is fine and dandy, because it isn't. There are still racist officers It is being replaced by the realisation that no officer with racist attitudes can expect to remain in the force. The surveys of black and ethnic minority opinion show that confidence amongst those communities in the police is at a significantly higher level than it used to be in the bad old days. But no one who cares about policing in Britain can be complacent. There are still racist officers. There are also officers who unconsciously treat those whose race is different to their own in unacceptable ways. Though their number is diminishing, there is still a great deal to do before we achieve a police force that is recognised by everyone as treating all members of our community fairly. I believe that the way this Government has restructured policing will help that progress to be achieved. We have replaced diktats from the centre with local control: Police and Crime Commissioners, directly elected by local people, now set your local force's priorities - and if those priorities do not match yours, for instance because they do not do enough to ensure that the police treat everyone fairly, then you can hold them to account and vote for a Police and Crime Commissioner who will do so. We have established the College of Policing to set professional standards for all officers, and to ensure that every new recruit, and indeed every experienced detective or bobby on the beat, understands and respects those standards. Every force needs to build trust and confidence, and to secure greater co-operation from ethnic minority communities Every force needs to build trust and confidence, and to secure greater co-operation from ethnic minority communities. I have never thought that those goals can be achieved by having teams of people with titles such as "equality and diversity officer." Our reforms have been dedicated to making the police accountable to the people. I believe that, in time, the result will be police forces that are much more representative of the communities they serve, and which treat everyone with decency, respect and justice. When that goal is finally achieved, it will be a fitting way to commemorate Stephen Lawrence.