Baroness Doreen Lawrence has said she cannot grieve until full justice is achieved.
The review was launched after a BBC investigation named a sixth suspect in the 1993 murder in Eltham.
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 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.
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.”
