Cressida Dick, an assistant commissioner of the Metropolitan police, explains how things have changed since the 1993 killing

All murders have a dreadful impact, on those who loved or knew the victim, witnesses and, frequently, on the local community. Some, such as those committed by the Yorkshire Ripper, Peter Sutcliffe, or the murderer of Victoria Climbi?, have a further impact by leading to substantial changes in practice by the police or beyond.

Some, such as the murder of Damilola Taylor, or so-called "honour" killings, are particularly shocking because of the light they shed on society's problems.

But no murder in modern times, or in the whole history of the Met, has ever had the impact of the killing of Stephen Lawrence.

No murder has been subject to such extraordinary levels of scrutiny over such a long period. And no murder has resulted in such wide-ranging changes in the police, the law, government and other agencies and society itself.

The Macpherson inquiry into the murder reported in 1999. It made 70 recommendations affecting policing, the criminal justice system and other institutions. It was not uncontroversial. Many in policing and outside objected to its tone and some of its findings. Doreen Lawrence, Stephen's mother, said it only "scratched the surface".

But the recommendations for policing were wholeheartedly accepted and implemented by the leadership of the Met and brought about fundamental changes to policing in the UK and internationally.

Many of the recommendations were about police skills, capacity and capability. Changes such as better emergency life support training for all officers have led to hundreds of lives being saved by police. Profound changes in the generation and use of intelligence, and adopting an open mindset to investigations and reviews, has vastly improved the quality of investigations and reduced the likelihood of miscarriages of justice.

Homicide investigations and the response to other critical incidents are better led and focused, much better resourced and supported by effective systems and more highly trained investigators. London's homicides have become much more complex as the population has become more transient and international, and yet the Met's murder investigations today are the envy of law enforcement worldwide.

Crucially, they maintain the confidence of families and communities from all backgrounds. Highly trained family liaison officers are deployed in cases of unexpected violent deaths, from terrorist incidents to road collisions. I frequently meet bereaved families, as I did on the 10th anniversary of 9/11, who have nothing but praise for the service they have had from their liaison officer.

Trident, the Met's highly acclaimed response to gun crime, was born out of the lessons of Lawrence. Racist incidents and other hate crimes are investigated with a sensitivity, seriousness and success unrecognisable from that which prevailed when Stephen died.

The Met's internal culture has also changed. The workforce is much more diverse and the Met celebrates that diversity, recognising its importance in being able to recruit and retain the best people, and in being much more representative of Londoners while being sensitive to their needs. The use of independent advisers from all communities has led to much more effective involvement of the public in policing, better consultation and engagement and quicker organisational learning.

The results speak for themselves ? well over 90% of homicides are detected, as are more than 50% of racist incidents. Black and minority ethnic (BME) communities have confidence in their police which is very nearly as high as that of other communities, and our recruiting from ethnic minorities is at an all-time high. Around 3,100 (9.5%) of our officers are from BME backgrounds.

The inquiry also resulted in the founding of the Independent Police Complaints Commission and important legal changes such as the Race Relations Amendment Act, racially aggravated offences and the "double jeopardy" provisions used in this case in relation to Gary Dobson.

As Jack Straw said, the process of the inquiry "has opened all our eyes to what it is to be black or Asian in Britain today".

In its recommendations and commentary, the inquiry challenged all institutions and society as a whole and contributed hugely to changing attitudes to race and racism.

Of course, not everything has been resolved. In policing, stop and search remains controversial in some communities, there is currently much examination of police-community relationships in London and ? as in other aspects of the criminal justice system and in wider society ? "disproportionality" between black and Asian and white remains.

But I believe the Met can be proud of how it has been transformed in attitudes, practice, training and professionalism. The changes are deeply ingrained and largely taken for granted by our young people.

Neville and Doreen Lawrence suffered the horror and injustice of the loss of a much-loved son in an appalling, unprovoked, violent attack. They have campaigned tirelessly for justice to be done and for policing and society to change for the better. Today marks another milestone in their long journey.

We should be very grateful to them, and to those who have supported them, that Stephen's legacy has been such a force for good and will continue to be so in the future.

Cressida Dick is an assistant commissioner in the Metropolitan police