POLICE would have faced tremendous difficulties in successfully building a case strong enough to bring about a successful prosecution over the murder of Ann Heron.

The decision to look again at the murder - committed nearly 16 years ago - was prompted partly by technological advances which police hoped would bring them close to the killer.

Ian Shaw, who manages Teesside University's centre for forensic investigations, would not comment specifically on Ann Heron's case, but said: "In general terms, people always assume that you are always going to be able to deploy the latest and newest scientific techniques successfully on so-called 'cold cases', but that is not always so.

"It may be that the material gathered at the time has deteriorated to the point where you cannot get useful results from it.

"Or, because of the way certain things were done years ago, you might not be able to rely on evidence you can uncover using today's techniques."

He added: "Whenever you revisit old cases, you are always alive to the fact that you are using super-sensitive techniques and that the methods of investigation and recovery at that time would be methods which would not recognise the possibility of obtaining results in the way we do today.

"Every police force in the land has looked at undetected murders and other serious crimes with a view to seeing whether they can be cleared up in this way.

"But there will be always be difficulties."

Asked whether scientific advances were seen as a panacea to solving old crimes, Mr Shaw said: "There is always the tendency to over- exaggerate and overdramatise the impact of forensic testing, particularly in the media - you need only look at television programmes such as CSI. Nevertheless, it has revolutionised crime investigations."

Mr Shaw warned that it was too easy to judge the standards of past investigations in comparison with those of today.

He said: "You cannot judge the way that things were done say 15 to 20 years ago with the way that things are done today.

"Those were proper and appropriate methods by the standards that were available at the time.

"If you look at a crime scene today, you will see crime examiners wearing white paper suits, masks, and boots - with similar precautions being taken in laboratories."

He also said that, regardless of the science, often simply trying to locate all the evidence posed its own problems.

He said: "Not all the material will rest with the police. It may rest with forensic science analysts and other organisations.

"Just trying to track down old information and locating items or exhibits can be an exercise in its own right and then you have to pull it all together - not the easiest task."

Forensic science consultant Geoff Knupfer, a former detective chief superintendent, said: "The dilemma with old cases is that when they were initially investigated, DNA evidence was not available in any shape or form or, if it was, you were very limited with what you could do with it.

"As a result, there is now an amplification process which is used called Low Copy Number (LCN), which involves enlarging tiny quantities of DNA from material gathered from crime scenes at the time.

"The danger in this is the possibility that you also amplify any contamination not detected from the time - which could be something as simple as a sneeze."