The flickering images being replayed in the control centre were crucial.

Even though it was difficult to distinguish the faces of the two teenagers, there was enough information on this piece of CCTV footage to help police make an ID.

They needed to. Helen Maughan's body had been found in the River Colne only hours earlier. It was odds-on the last people she had spoken to were those teenagers.

Which is why the police needed to find out who they were. The CCTV camera above Quilters pub at Colchester Middleborough - only a short distance from where the mother-of-two had been discovered in May last year - gave them everything they needed.

Identification quickly followed. Then the police - and, eventually, Chelmsford Crown Court - discovered the schoolboys had done more than speak to Helen Maughan. They had savagely killed her.

"There were many things which contributed to this murder investigation and having CCTV footage of the victim was one of them," explained Colchester Police's district commander Chief Inspector Adrian Coombs.

"It may not have brought the teenagers to trial, but it helped."

Yet not everyone sees it that way. Earlier this month, Metropolitan Police officers claimed CCTV had "failed to have a significant impact" on crime prevention.

A senior officer said only three per cent of street robberies in London were solved using CCTV images, despite the UK having more security cameras than any other country in Europe.

"I can only speak for Colchester," declared Chief Insp Coombs, "and here you have got to give some credit to our CCTV network.

"In the past three years there has been a 17 per cent overall reduction of crime in the town centre. Now, it's difficult to say how much of that reduction is down to CCTV, but I believe that if you put a CCTV camera in a certain location and publicise it, that will act as a preventative measure."

He wonders whether the CCTV network used by the Met is big enough - or sophisticated enough - for the job.

"That could be the problem," he pointed out.

"Here, we are covering a much smaller area, but we are covering it well. There are seven cameras in High Street alone and, with the latest (digital) upgrade, the picture quality is far better than it has ever been.

"Colchester is also keeping up with the latest technology. Some cameras now have 360 vision."

Since 2005, both the number of serious assaults and muggings in the town centre have each dropped by 24 per cent.

Bob Brookes, CCTV monitoring centre co-ordinator for Colchester Council, pointed out that in the last financial year, from April 1, 2007, to March 31, 2008, CCTV images helped in 550 town centre arrests.

"On 466 occasions the monitoring centre offered images and tapes to police to review in relation to offences, with officers taking away 291 sections of evidence," said Mr Brookes.

"But it isn't only a case of control centre staff just watching the screen. We are pro-active and work very closely with Colbac (Colchester Businesses Against Crime) and the town's Pubwatch members. We link up with many of the town centre's stores and shops to pass on information about people behaving suspiciously. These are people who have not committed a crime but look as though they might.

"It is both the cameras and our networking which, I believe, is acting as a deterrent and bringing down the crime figures."

And, as in the case of Helen Maughan, helping justice take its course.

HOW FAR IS COLCHESTER CCTV'S REACH?

Colchester town centre CCTV network covers a lot more than High Street, Head Street, Culver Square and Lion Walk Shopping Centre.

It takes in Southway, Balkerne Hill, North Station Road, Albert roundabout, East Hill to Priory Street, Queen Street, St Botolph's Street and Colchester Town station. There were plans to have a mobile camera at Colchester North station, but Bob Brookes, CCTV monitoring centre co-ordinator for Colchester Council, said the overhead wires "interfered with transmission".

All town centre underpasses have two CCTV cameras.

COLCHESTER AND CCTV

  • January, 1997: Colchester Council unveiled CCTV system in town centre - 100 cameras and state-of-the-art control centre in Angel Court
  • August, 1997: The number of crimes in town centre between January and August dropped by 38 per cent compared to the same period the previous year
  • January, 2000: For the first time crime in town centre lower than the rest of the borough. Amount of vandalism down, but assaults up. Police said this could be because more attacks were being spotted by CCTV operators
  • March, 2004: Colchester has one of the largest town centre CCTV systems in the UK - 128 static cameras and two mobile cameras
  • November, 2007: Blanket coverage of town centre via 150 cameras, including 26 owned by Lion Walk Shopping Centre and Culver Square which are linked to the network, but Colchester Council told system outdated and £300,000 needed for new digital technology. This would include special cameras with loudspeakers which allow operators to talk to people in the street
  • February, 2008: Colchester Council agrees £300,000 to update Colchester CCTV system. Includes enhanced visual quality for 16 cameras and digital recording for all 150 cameras.