The Metropolitan Police are being investigated for alleged corruption over their initial handling of the murder of black teenager Stephen Lawrence, the National Crime Agency (NCA) has confirmed.
The new investigation comes more than two decades after the 18-year-old was stabbed to death by a racist gang.
Any findings will be reported back to the police watchdog, and could result in criminal or misconduct proceedings where failures have been identified.
The investigation has been active for more than six months, but has only come to light today.
In a statement, the NCA said: "The National Crime Agency can confirm its investigation into alleged police corruption during the original investigation into the murder of Stephen Lawrence.
"The managed investigation for the Independent Police Complaints Commission (IPCC) is being led by Roy McComb, NCA deputy director for specialist investigations.
"The IPCC has confirmed Roy McComb's appointment by the Metropolitan Police Service, and the investigation became live on March 9 2015.
"Members of the Lawrence family, Duwayne Brooks (Mr Lawrence's friend and now local politician) and their legal representatives have already been spoken with by the Senior Investigating Officer, and we will continue to meet and update them as appropriate.
"No further details about the investigation are being provided at this time for operational reasons."
Stephen, 18, was stabbed to death by a gang of white youths as he waited at a bus stop in Eltham, south-east London, with a friend on April 22 1993.
It was more than 18 years before two of his killers - Gary Dobson and David Norris - were brought to justice.
The pair were jailed for life in January 2012 for their role in the attack.
A separate investigation is already being carried out by the IPCC, after Mr Lawrence's father, Neville, made a complaint in April about former Metropolitan Police commissioner John, now Lord, Stevens over claims he withheld evidence from the 1998 Macpherson Inquiry. The Met subsequently referred itself to the IPCC.
In an outline of its investigation, the watchdog said it would look at what information was known by Lord Stevens' office when his evidence was submitted.
In a letter to the inquiry, Lord Stevens said no officer or former officer involved in giving evidence at the inquiry was under investigation for corruption.
But a second review of the case last year by Mark Ellison QC found corruption allegations about a Metropolitan Police detective who worked on the original investigation into the killing should have been revealed to the inquiry.