IT was a microscopic spot of blood discovered on a pillowcase that could not be seen by the human eye.

Found in Julie Smailes' bedroom, the blood proved, almost eight years after her tragic death, that the 27-year-old had been murdered by drug user John Thompson.

In 1996, detectives heading the search for her killer had examined the bed linen for clues.

The pillowcase was stained with Miss Smailes' blood, but DNA technology at the time was unable to detect the vital evidence that could have led them to the murderer.

Another splash of blood found on patio doors at her home also revealed the same DNA sequence as the one discovered in her bedroom.

Detectives believe Thompson cut himself while he was carrying out the violent assault on Miss Smailes. She had been stabbed more than 50 times and was bleeding profusely.

Using newly refined techniques in DNA, forensic scientists discovered her killer's blood was among the blood found on the pillowcase.

Though DNA had first been used as a crime detection tool in 1986, it had not been developed sufficiently to detect microscopic samples of blood at the time of her death ten years later.

Scientists were only able to carry out DNA profiling on larger amounts of fluids, such as blood, semen and saliva, and could not detect any DNA sequences. In many cases, laboratories were unable to determine what the fluid was.

DNA can be found in tissues, bones and biological fluids in the body and all the DNA taken from different areas of the body is the same. The DNA that humans receive from their parents is unique, apart from identical twins, and patterns can be used to establish paternity and maternity.

In criminal cases, scientists are able to compare DNA profiles taken from a crime scene with information stored on the DNA computer database that holds profiles of convicted offenders.

In the case of Miss Smailes, scientists may have been able to match the DNA profile found at the murder scene to a profile on the DNA database.

Thompson was a convicted offender. He had served prison sentences for crimes of violence and was released shortly before the murder of Rachel Tough.

It is understood scientists at the Forensic Science Unit were able to use a method called low copy technique to assist in Miss Smailes' case.

Ian Shaw, senior lecturer in forensic science at Teesside University, said though it was not a new way of developing DNA profiling, it was an advancement of procedures scientists already used.

He said: "It is a technique that improves the sensitivity of existing DNA profiling so you can obtain results from things in the past that you previously could not obtain results from.

"It is only used in certain circumstances, mostly in serious crimes, and is not used routinely as in most cases it is not necessary.

"It is usually used to assist in cases from the past that happened prior to the technology being developed, or in cases where at the time DNA tests were not sufficiently sensitive to produce results."

Using low-copy techniques, scientists can amplify the amount of DNA, which has the ability to make copies of itself, so that scientists can get a sufficient amount of DNA to analyse.

Mr Shaw said: "DNA has been a major advancement and is obviously another tool that can be used in policing."