Leading article: The Lawrence case is far from over

It took the full weight of the Macpherson inquiry to expose the institutional racism that hampered the Metropolitan Police investigation into the murder of Stephen Lawrence. Now, fully 19 years after the teenager's fatal stabbing, evidence from secret Scotland Yard files, published in this newspaper today, suggests there may be more – and worse – to come.

That one of the leading detectives on the Lawrence case was widely suspected of being a "major player" in a corruption ring "operating as a professional organised crime syndicate" is shocking enough. But the accusation that a crooked relationship between Detective Sergeant John Davidson and the drug-dealing father of one of the prime suspects may have had a bearing on the investigation – and that the Met's anti-graft squad knew of the alleged links and deliberately kept them back from the public inquiry – is more alarming still.

So far, the Met is sticking to the same line it took with Sir William Macpherson: there is evidence that DS Davidson was corrupt, but nothing to link those activities to the Lawrence case. With supergrass Neil Putnam claiming otherwise, and discrepancies over the debriefing process, that is simply not good enough.

The claims heap pressure on the Met, which is already reeling from last week's Leveson Inquiry session revealing a "network of corrupted officials" accepting bribes from The Sun in return for "salacious gossip", and was buffetted further yesterday by the appearance of Paul Stephenson – the former Commissioner forced to resign over his links to Neil Wallis – to answer questions about his relationship with the former News of the World executive arrested over the scandal.

The murder of Stephen Lawrence, and the flawed police investigation that followed, are stains on British society and British justice. With only two of the five people involved in the killing convicted, it cannot be over yet. And in the light of the latest appalling allegations of corruption, there must be a full, independent inquiry into the activities of the Met investigation team. No more prevarications. No more cover-ups. We owe it to Stephen Lawrence, and to his parents.