Met commissioner promises to continue search for evidence, even though Gary Dobson and David Norris convicted

The three remaining key suspects for the Lawrence murder were left in no doubt: keep looking over your shoulders.

Speaking publicly for the first time about the case on Wednesday, the commissioner of the Metropolitan police, Bernard Hogan-Howe, promised that his officers would continue to search for evidence against others, even though Gary Dobson and David Norris have been convicted.

"The other people in the murder of Stephen Lawrence should not rest easy in their beds," said Hogan-Howe. "We are still investigating this case. If anybody out there has any information, even after all this time, please tell us. We will do the rest." The judge, Mr Justice Treacy, told the police after sentencing to keep the murder file open. "On the evidence before the court there are still three or four other killers of Stephen Lawrence at large," he said.

The other three men who were named as "prime suspects" in the Macpherson report are Neil and Jamie Acourt and Luke Knight, who, along with Dobson and Norris formed the racist gang who marauded around Eltham in the early 90s. There has been mention in the past of a fourth suspect but he has never been identified by police.

But while Hogan-Howe appeared bullish about the ongoing inquiry, sources closer to the investigation have acknowledged they have exhausted all live lines of inquiry. The latest cold-case scientific review costing ?3.8m submitted all exhibits from the Acourts and Knight to a thorough review. But nothing was found to enable police to charge any of them. Scientists on the inquiry said they had exhausted all avenues and cutting-edge science had failed to uncover any evidence to put the three men in the dock.

The only hope police have is changing allegiances from associates of the gang or ex-girlfriends who may have witnessed and perhaps recorded on a mobile phone someone's confession or offhand remark. But for 18 years despite, no one has broken the vow of silence among members of the gang and their close associates.

Neil Acourt was always regarded by police as the leader of the gang. Obsessed with knives, he exposed a vicious racism in the surveillance tapes made by the police in 1994. He is seen in the footage thrusting a knife at an imaginary person, and later skilfully putting the same large knife down his trousers before he goes out into the night. He is filmed talking about "chopping up" black people, and referring to them as niggers.

Acourt has not moved far from the scene of the crime, or the rundown terraced house he lived in at the time. It was inside his family home at 102 Bournbrook Road on the Brook estate in Eltham that police found a stash of weapons, including a knife behind the TV, another Gurkha-type knife in one of the padlocked bedrooms, a sword under the cushions of a sofa as well as knives in another bedroom and an airgun-type revolver.

Today he lives a couple of miles away in a newly refurbished bungalow on the outskirts of Sidcup in Kent. Well built from his hobby of body building, he lives with his girlfriend. When the Guardian tried to contact Acourt, his Mercedes 4x4 was parked right outside his front door, apparently so that he can avoid being photographed as he leaves his home.

He has maintained contact with the other suspects and was jailed in 2002 for the racially aggravated harassment of an off-duty black police officer ? a crime committed with David Norris. A year earlier he was convicted of possessing an offensive weapon ? a baton he claimed he kept for his own protection.

Acourt uses his mother's maiden name, Stuart, to avoid unwanted attention. But some believe he thrives on the notoriety he has gained over the last 18 years. He told Martin Bashir in an interview the five suspects gave in 1999 that he would not stand for trouble from anyone. "We're seen as murderers, big-time gangsters, just killers. We're looked upon as scum.

"If someone put trouble in my way I would not stand for it, simple as that."

A mile or so away his younger brother, Jamie Acourt, lives in a three-bedroomed terraced house in a tree-lined street. He has two children, whose scooters lean on the outside wall of the property. His girlfriend has recently set up a business selling designer baby clothes, according to friends in the street. He does not appear to work. "I'm not sure what he does for a job," said one neighbour. "He loves playing football, and he is always off doing that."

Since the Lawrence killing he has been convicted of one offence ? stealing 32 soda siphons from a drinks warehouse in 1999 with David Norris.

Luke Knight has always been considered as the fifth suspect and was mentioned as a suspect in the court case. However, the Guardian understands the police may no longer believe he was there.

His family say his life has been ruined by the notoriety associated with his name. Now 35, he lives in Eltham and is said to be paranoid and depressed.His sister Lisa is reported saying: "It's never going to end. They have all been guilty until proven innocent. We have all been affected by this ? it's horrendous."

Several years ago Knight applied to Greenwich council to be rehoused because he said he was the subject of racial abuse.