Doreen Lawrence has called on the Metropolitan Police to "be honest" about the likelihood that anyone else involved in her son's murder will be brought to justice.
Scotland Yard says the probe into Stephen Lawrence's racially-motivated killing 25 years ago remains "in an active phase", however his mother said she suspects detectives have run out of lines of inquiry.
Speaking to the Daily Mail, Baroness Lawrence said she believes the Met is concerned about her public reaction should they decide to close the case.
She also suggested that she was ready to begin to move on from her tireless pursuit of justice for her son and dedicate her time to her family and grieving.
"I don't think they (the police) have any more lines of inquiry. They say they're carrying on the investigation, but carrying on doing what?" the Labour peer said.
"If they've come to the end, they should be honest -- say they've come to an end and stop."
"I think they're carrying on pretending everything's fine because they don't want to hear what I'll say if it is stopped."
To date, two people have been convicted over Mr Lawrence's killing in Eltham, south-east London, on April 22 1993.
In 2012, Gary Dobson and David Norris were found guilty of murder under joint enterprise and jailed for life.
Six years on from the convictions, Baroness Lawrence said she was acutely aware of the cost of the ongoing investigation to the taxpayer.
Detectives believe Mr Lawrence was stabbed to death by a group of up to six white men in the unprovoked racist attack as he waited at a bus stop with a friend.
Failures in the police response to Mr Lawrence's murder sparked outrage and prompted a series of inquiries.
His parents launched a failed private prosecution against Dobson, Norris and other suspects in the case in 1994.
Then, in 1996, a murder trial at the Old Bailey against Dobson and two other defendants collapsed after identification evidence was ruled inadmissible.
Following a 1997 inquest, a jury concluded Mr Lawrence was "unlawfully killed by five white youths".
And in 1999 findings of a judicial inquiry by Sir William Macpherson accused the Met of "racism, professional incompetence and bad leadership".
Baroness Lawrence said the failure to bring all those involved in her son's murder to justice stemmed from the "incompetent and racist" behaviour of some officers involved in the original probe.
However the peer said the 2012 convictions had lessened some of the anger she feels.
Meanwhile, after 25 years of tireless campaigning for justice for her son, the grandmother said it was time to grieve for her son and focus on her family and herself.
A Scotland Yard spokesman said: "The investigation into the murder of Stephen Lawrence remains in an active phase. The Met continues to hold regular meetings to update the family."