A report by barrister Mark Ellison QC published yesterday found that one of the officers on the original investigation into his death, detective sergeant John Davidson, may have acted corruptly.
Baroness Lawrence said she had always believed that there was corruption in the police investigation into her son's murder, and was on the verge of breaking down as she made an emotional statement.
Stephen was murdered by racists at the age of 18 in Eltham, south-east London, in April 1993, and it took nearly 20 years for two of the gang of up to six killers to be brought to justice.
It was claimed that Mr Davidson had admitted having a "corrupt connection" with Clifford Norris, the gangland boss father of David Norris who was convicted of Stephen's murder in 2012.
Baroness Lawrence said:"It's been 21 years of struggle and no family should have to do that. It's the job of the justice system and the police service to give service to the whole community not just to one section.
"We weren't asking for anything special, just for something that we should have had."