Scotland Yard has admitted it has no new lines of inquiry in the investigation into Stephen Lawrence's murder.
The force said on Wednesday that unless detectives receive new information the investigation is "unlikely to progress further".
Last week, Stephen's mother Doreen told the Daily Mail that the investigation should end.
Stephen's father, Neville Lawrence, said he remains hopeful that with the publicity around the 25th anniversary of Stephen's death and the BBC documentary that someone will come forward.
He told the Press Association: "I'm hoping that somebody, somewhere that may have some information might just come forward. I'm hopeful.
"The threat of anything happening to them now isn't as great as it was in the early days. I'm pleased that they (the police) tried all different options and are still trying after all these years."
Baroness Lawrence said: "They say they're carrying on the investigation, but carrying on doing what?
"If they've come to the end they should be honest, say they've come to an end and stop."
In a statement the Met said that after "numerous reviews and every possible advance in forensic techniques, the Met investigation team is now at a stage where without new information the investigation is unlikely to progress further, and this was explained to the family earlier this year."
Chris Le Pere, the senior investigator, said: "We understand that 25 years is a poignant anniversary of the tragedy of the murder of Stephen, and our thoughts remain very much with those who loved him, and feel his loss.
"With the approaching anniversary and airing of a documentary, Stephen: The Murder That Changed A Nation, there is still the opportunity for someone who knows what happened that night, to have a conscience and come forward. I would say to you, it is never too late to do the right thing.
"We continue to speak to Baroness Doreen Lawrence and Dr Neville Lawrence to update them on the current Met position."
Stephen was murdered by a gang of racists in Eltham, south-east London, on April 22 1993.
Of his five or six attackers, two are serving life sentences for his murder - Gary Dobson and David Norris - who were jailed in 2012 after an Old Bailey trial that hinged on tiny traces of forensic evidence.
His parents took a private prosecution against three men - Dobson, Luke Knight, and Neil Acourt in 1996, but the case collapsed.