The former Metropolitan Police Deputy Assistant Commissioner, Brian Paddick, has told Daybreak that police are still appealing for information on the death of Stephen Lawrence, twenty years on from his death.
He said: "As time passes people will be less reluctant to keep silent, maybe their conscience will get to them and they will come forward."
Neville and Doreen Lawrence battled for nearly two decades for justice for their son, and they finally saw Gary Dobson and David Norris jailed for his murder in January last year.
Stephen Lawrence, an aspiring architect, was set upon by a gang of five or six thugs, but the remainder of the killers have never been punished. The detective leading the investigation insisted that the inquiry is still live and that his team will follow any leads that come up.
– Detective Chief Inspector Clive Driscoll
It's a live investigation. All avenues of the investigation will be left open and we will revisit them whenever we feel we have to. You never close your mind to anything. We will endeavour to follow all the leads that we can.
The mother of Stephen Lawrence, Doreen, will be joined by friends and relatives at the memorial service which is takes place near Trafalgar Square in central London. A number of high-profile supporters of the charitable trust that she set up in her son's name are also expected to attend.
Stephen's father, Neville, has chosen to remember his son privately in Jamaica today, taking flowers to his grave and saying a prayer with a friend who is a pastor.
A number of high-profile public figures including Metropolitan Police Commissioner Sir Bernard Hogan-Howe are expected to attend today's memorial service.
A poster has been put up in New Scotland Yard featuring a personal message from Sir Bernard about the investigation. It reads:
– Metropolitan Police
Twenty years ago the Lawrence family lost their loved son, Stephen. We let them down by not catching his murderers. Then last year we finally brought two of his killers to justice. The Met won't forget Stephen Lawrence.
David Cameron says the murder of Stephen Lawrence sparked "monumental change" in British society. The Prime Minister made the comments ahead of today's memorial service on the 20th anniversary of the teenager's death.
David Cameron praised the tireless efforts of Stephen's family in their campaign for justice, but acknowledged "more still needs to be done".
He added: "The senseless killing of Stephen Lawrence in 1993 was a tragedy. 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.
"I believe that many of those questions have been answered: from improved community relations to more accountability in policing. Much has been achieved, but we know that more still needs to be done. We owe this to the memory of Stephen."
A memorial service will take place today to mark the 20th anniversary of the death of Stephen Lawrence, the teenager murdered by a racist gang in south-east London.
18-year-old Stephen was murdered as he waited for a bus in Eltham in April 1993. The police investigation into his death was marred by incompetence and allegations of racism, and it took 19 years to bring any of his killers to justice.
Read Julie Etchingham's blog: Remembering Stephen Lawrence.