Baroness Doreen Lawrence has described a new official review as the “last opportunity” for justice.
The review, conducted by the College of Policing, was launched after a BBC investigation named a sixth suspect in the 1993 racist murder in Eltham, south London.
Baroness Lawrence told the BBC: “This is the last opportunity that we’re going to have to get the complete justice that I think Stephen so deserves.
“So I would like to ask them, whatever they felt at the time, or whatever happened if they tried to help, please come forward now.”
The College of Policing confirmed the review is independent of the Metropolitan Police.
Investigators are examining Met Police files to identify any outstanding lines of inquiry.
The review, announced last year, follows reports of police failings and an apology to Baroness Lawrence from Met Commissioner Sir Mark Rowley.
After negotiations, the Met agreed to key demands from the Lawrence family, including the involvement of retired detective Clive Driscoll, who secured two convictions in the case.
In 2014, Mr Driscoll was replaced as senior investigating officer by the Met before he could complete his inquiry.
The review team will be led by a recently retired senior detective from outside the Met.
It will examine whether any investigative opportunities were missed or mishandled, and will focus in part on news reports by the BBC.
If new lines of inquiry are found, they will be referred to an independent investigative body.
A Met Police spokesman said its goal remains “to achieve the arrest, prosecution and conviction of all of those responsible for Stephen’s murder”.
He said: “The review is being led by an experienced investigator working for the College and will focus on identifying any outstanding lines of enquiry which could reasonably lead to a suspect being brought to justice.”
