NOTHING like the savage murder of PC Keith Blakelock had been seen since 1833, when PC Robert Culley was stabbed to death during riots in Clerkenwell, central London.

PC Blakelock and his unit were ill-prepared for what they were to encounter on the Broadwater Farm Estate on the night of Sunday, October 6, 1985.

The 40-year-old, who was originally from Sunderland, had been working as a beat bobby in Muswell Hill. He had no formal riot training and was armed only with a truncheon and had a shield and helmet for protection.

His unit had been sent to help firefighters put out a fire in a supermarket, but the unit became surrounded by rioters and had to battle their way out of the building.

PC Blakelock had stayed at ground level with a colleague to keep their exit clear. As the unit emerged from the building into the dark, he was set upon by a large crowd armed with an assortment of weapons, including knives and machetes.

He was stabbed more than 40 times to shouts of “kill the pig” and an attempt was made to decapitate him. His colleague PC Richard Coombes was also attacked but managed to survive.

The riots came as tension between the community and police reached breaking point with the death of Cynthia Jarrett from a heart attack during a search of her home in Tottenham.

Since the murder, there have been three separate investigations, with the most recent culminating in the trial of Nicky Jacobs, who was acquitted of murder yesterday.

These investigations, according to Mr Jacobs’ defence, only served to alienate the community more.

He was the seventh person to be charged over the mob killing, as previous attempts to secure a successful conclusion to the case foundered.

Among the accused were three youths who never faced trial after a judge ruled their questioning was inadmissible.

In March 1987, Winston Silcott, Mark Braithwaite and Engin Raghip were found guilty of the murder.

But their convictions were quashed four and a half years later, after forensic tests on pages of key interview records suggested they had been fabricated.

Mr Silcott later accepted £50,000 compensation from the Metropolitan Police for their part in his wrongful conviction.

In January 1993, in a bid to encourage witnesses to come forward, the controversial decision was taken to draw a distinction between so-called “kickers” and “stabbers”.

POLICE offered immunity to people who did not use weapons in the attack on PC Blakelock – among them were the witnesses referred to as John Brown and Rhodes Levin who were to give evidence against Mr Jacobs.

Some of the informers were also paid for their co-operation.

Meanwhile, in 1994, charges were brought against two officers involved in the original inquiry. They were accused of fabricating evidence but were both cleared at the Old Bailey.

In 2003, Scotland Yard reopened the murder investigation and made a series of arrests in connection with PC Blakelock’s death and the attempted murder of his colleague PC Coombes.

In 2005, police released images of Mr Blakelock’s blood-stained overalls in a bid to prompt fresh witnesses to come forward.

Investigators repeatedly said people in the area had information about the identity of the killers they have not shared with police.

Mr Jacobs was interviewed again by police in 2010 but was only charged last year, prompting his lawyer, Courtenay Griffiths QC, to question why it had taken so long.

In fact, the defendant, who was 16 at the time, was first arrested over the murder five days after the riots.

He was charged with affray and later sentenced to youth detention for eight years, but was eventually reduced to five on appeal.

Police had known about a rap poem in which Mr Jacobs allegedly described the murder while behind bars since it was found in 1988.

By that time, police also had evidence he was on the Broadwater Estate the night of the riots.

By 1994, police had witnesses Mr Brown and Mr Levin, who claimed to have seen Mr Jacobs with a weapon during the attack on PC Blakelock.

And by 2000, police knew about a comment Mr Jacobs made to a police officer claiming involvement in the murder.

Five years ago another witness, known as Q, came forward alleging he had seen Mr Jacobs attacking PC Blakelock with a weapon.

During his closing speech Mr Griffiths condemned efforts to convict Jacobs 28 years later as “deplorable”.

However, prosecutor Richard Whittam QC urged the jury to set aside emotions and try Mr Jacobs on the evidence alone.

The jury of five women and seven men took six hours to find Mr Jacobs not guilty of taking part in the attack.