Detectives have decided that Gary Dobson and Luke Knight were probably not part of the racist gang that stabbed to death the black teenager in Eltham, south-east London, in April 1993.
This startling conclusion overturns long-held assumptions about the identity of the murderers, and means that as many as three other suspects could be prosecuted for the killing.
Duwayne Brooks, Stephen's friend and the main witness, told police in his first statement about the attack that it was carried out by six white youths. Other witnesses have suggested that there may have been six, rather than five, people involved.
Detectives are now focusing their attention on several local men who were known associates in 1993 of the remaining three - Jamie Acourt, his brother, Neil, and David Norris.
They are also examining allegations that some of the suspects may have been involved in a series of violent attacks carried out in the area in the year before Stephen was killed.
The cases include the stabbing of a white teenager, Darren Witham, in May 1992, and an incident in November 1992 in which a black youth, Kevin London, was allegedly threatened with a knife in Eltham.
Mr Dobson and Mr Knight, both 23, stood trial with Neil Acourt at the Old Bailey in 1996 after the Lawrence family mounted a private prosecution against the five. They were acquitted of murder on the judge's direction after Mr Brooks's evidence was ruled unreliable.
All five of the original suspects were branded murderers two years ago on the front page of the Daily Mail.
John Grieve, one of Scotland Yard's most experienced detectives, who took over as head of the Lawrence murder squad a fortnight ago, has said that he is challenging all previous assumptions about the case.
The Acourts and Mr Norris are still regarded as prime suspects. Jamie Acourt, 22, and Mr Norris, 23, have never stood trial for Stephen's murder, but - because of widespread publicity - could probably argue that they could not receive a fair hearing. Recent reports suggesting that the three acquitted in 1996 could face other charges have been dismissed by legal experts.
In 1993, the Acourts and Mr Norris were the prime movers in a gang that had a shifting membership of up to a dozen youths united by violent and racist tendencies and, in some cases, by blood relations.
Mr Knight was a particular friend of Jamie's, while Mr Dobson was close to Neil. The five had known each other for years.
Police were given the names of the five by local informants in the early days after Stephen's murder. But they were also given the names of several other youths in the Acourts' gang.
Detectives believe that it may now prove fruitful to scrutinise some of the earlier incidents of violence.
One detective said: "The question is: how do you view the murder of Stephen? Is it an isolated incident, or is it part of a composite series of events?"
Darren Witham claims that he was stabbed in the arm by David Norris outside a shop in Chislehurst, south-east London. He says that he was trying to help his older brother, Terry, who was being attacked by a group that allegedly included Jamie Acourt.
Mr Norris was charged with the stabbing, Mr Acourt with possession of a truncheon. But the Crown Prosecution Service dropped the charges in early 1993, before Stephen was killed.
Kevin London, a black youth, claims that he was threatened in Eltham by a group that included Mr Dobson and Neil Acourt. He alleged in a documentary screened last week that Neil Acourt lunged at him with a knife.
As well as looking at these and other cases, Mr Grieve's squad is planning to revisit potential witnesses and informants in Eltham who did not co- operate with the original police investigation of Stephen's murder.
Detectives believe that allegiances have changed over the past six years, and that women in particular - ex-girlfriends, sisters and mothers - may now be willing to help police.
New scientific techniques mean that it may also be worthwhile to submit forensic evidence to further tests.
Mr Knight was picked out at an identification parade by Mr Brooks in June 1993. Mr Dobson attended parades, but was not picked out.
The police surveillance video shot at Mr Dobson's flat in late 1994 shows both men taking part in conversations peppered with sadistic racial abuse.
However, Mr Dobson, who is believed to have had black friends, shows less enthusiasm. At one point he says that "some (blacks) are all right", to which Neil Acourt replies that black people are "c....".
Mr Dobson and Mr Knight are the only two of the group who answered questions when they were arrested. Both told police that they were at home on the night of the murder, which was corroborated by their parents. Mr Dobson later added that he went out shortly before midnight to visit the Acourts.
At one time, Mr Dobson was regarded by detectives as a possible "weak link" who might crack under pressure and give them information.
Mr Knight's family used to live in Well Hall Road, the street where Stephen was attacked. Police believe that the gang came across Mr Brooks and Stephen after emerging from Mr Knight's house - but they now think Mr Knight stayed at home.Reuse content