POLICE said last night they were confident of bringing the killer of PC Keith Blakelock to justice - 19 years after he was hacked to death with a machete.

The Sunderland-born, 40-year-old policeman was murdered during the Broadwater Farm riot, in north London, in October 1985.

Yesterday, detectives began searching 16 Willan Road in Tottenham, north London.

They said they were convinced that vital evidence is buried in the rear garden.

Commander Andy Baker, the Metropolitan Police's head of homicide said: ''We are very confident. This is about our ethos of relentless pursuit in any murder case.''

He remained tight-lipped about what police expect to find amid growing speculation that detectives had pinpointed the murder weapon.

Father-of-three PC Blakelock was hacked to death by a mob wielding machetes and knives.

Both he and PC Richard Coombes were attacked as they tried to protect firefighters. PC Coombes, now in his 50s, was seriously injured and never returned to duty.

The latest painstaking search is taking place only a stone's throw from the murder scene. Material will sifted and examined under forensic conditions.

Weapons were recovered after the murder. PC Blakelock's helmet was never found. It is thought that bloody clothing from the killers could still be recoverable and tested using the latest DNA technology.

Detectives would not discuss any suspects, if the person who lived at the address at in 1985 had been tracked down or if they are important to inquiries.

The current residents moved into the house in the late 1990s and are not suspects.

Mr Baker said: ''If we find out who the killers are we will put that before the Crown Prosecution Service and they will decide on that independently.''

Winston Silcott was convicted in 1987 along with Mark Braithwaite and Engin Raghip of the murder but in 1991 their convictions were overturned on appeal because of ''unsafe'' police evidence.

Two officers involved in the original Broadwater Farm inquiry - former Detective Chief Superintendent Graham Melvin and ex-detective inspector Maxwell Dingle - were charged with fabricating evidence but were cleared at the Old Bailey in 1994.

The re-investigation into the murder and attempted murder was announced in December.

More than 3,000 leaflets were dropped on the estate and neighbouring areas to warn residents of the disruption.

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

He was released from prison in October after serving a sentence for the murder of Anthony Smith, 24, whom he stabbed to death in a fight in December 1984.