Thirty years ago PC Keith Blakelock was stabbed in the Broadwater Farm riots in Tottenham, north London. Despite numerous investigations no-one has ever been convicted of his murder.
On 5 October 1985 four policemen burst into the home of Broadwater Farm resident Cynthia Jarrett looking for stolen property.
They failed to find any, but Ms Jarrett had a heart attack and died.
Her death was only weeks after riots in Brixton, south London, which happened following the accidental shooting of Cherry Groce by police officers.
On 6 October, following Ms Jarrett's death, her family met with police and demanded an inquiry. They made it clear though that they did not want any kind of public disorder.
At 18:45 GMT that day, however, police were called to Mount Pleasant, Willan Road and The Avenue.
Once there, they were pelted with bricks, bottles and petrol bombs. Cars were overturned and set alight, as were shops and other buildings.
In the hours that followed, up to 500 officers were drafted in, battling with rioters throwing bottles and cans from the walkways within the estate.
At about 22:15 BST, PC Keith Blakelock was repeatedly stabbed and, a court later heard, attempts were made to decapitate him.
PC Blakelock, who was from Sunderland, was trying to protect firefighters tackling a blaze. He died later in hospital.
By midnight, 58 policemen and 24 other people had been taken to hospital.
Police in riot gear occupied the estate for two months after the disturbance, using police dogs, helicopters and surveillance equipment.
In 1987, Winston Silcott, Engin Raghip and Mark Braithwaite were convicted of PC Blakelock's murder.
However, their convictions were quashed by the Court of Appeal in 1991, after questions were raised about the way police interviews were carried out.
A second investigation between 1992 and 1994, which offered immunity from prosecution for those in the mob who had kicked rather than used weapons on PC Blakelock, did not result in prosecutions.
Two police interrogators, Det Ch Supt Graham Melvin and Det Insp Maxwell Dingle, were also charged with perverting the course of justice over concerns about fabricating evidence. They were acquitted in July 1994.
Nineteen years later, Nicholas Jacobs, 44, of Hackney, was charged with PC Blakelock's murder.
In April last year, an Old Bailey jury cleared Mr Jacobs by a majority verdict.
Following the case, the Met defended its decision to pursue a conviction against Mr Jacobs, and said it would not be deterred from future investigations.
A force spokesman said the investigation into the murder of PC Blakelock remains open.