DNA evidence

Where the authenticity in the chain of custody of a DNA sample cannot be established, DNA evidence obtained from it is rendered useless. However, even if the judge decides to accept it as admissible evidence, the defence still has a good opportunity to reduce the weight of such evidence on cross-examination. On the other hand, the advanced technologies available at the present time to the forensic science, allow scientists to obtain a DNA profile even from samples that have been naturally contaminated. The process, by which such DNA profiles are obtained, is known as Low Copy Number (LCN) DNA and it is described as the most sophisticated DNA profiling service to date16. Significant characteristic of this process is that it can also produce a result from samples not necessarily containing human tissue, such us hair, bones and teeth.

Currently in England LCN DNA has been used in the most serious cases. Peter Shand, head of a Hampshire police operation to find DNA links between unsolved sex attacks, added: “There is a waiting list of cases for LCN. At the moment, every case that is looked at has to be of a very serious nature. If it was a burglary, they wouldn’t look at it. The priority is for unsolved murders, rapes or armed robbery.”

One of the first applications of LCN DNA was in R v Hanratty18. In that case, the brother of the deceased appealed against his conviction for murder in 1962, on the grounds that the in the first trial the judge failed to give correct directions to the jury, and because the prosecution failed to disclose crucial for the verdict evidence. The prosecution sought to adduce fresh DNA evidence that would establish that Hanratty was correctly convicted of murder. Therefore, it was asked from the prosecution for permit to exhume the body of Hanratty in order to produce and compare his DNA profile. The defence contended that DNA evidence would have been contaminated and therefore should not be rendered admissible.

The Court of Appeal rejected the possibility that DNA evidence could have been contaminated and evidence was rendered reliable, with respect to the results of the powerful DNA LCN analysis. Although considering the fact that the fresh DNA evidence was aimed to attack the grounds of appeal, the court ruled that the Crown had the right to adduce fresh DNA evidence, in accordance with section 23 of the Criminal Appeal Act 1968, as soon as it was in the interest of justice.

Whilst DNA evidence boldfaced the correctness of Hanrattys’ conviction, in R. v Shirley19, it pointed out a significant miscarriage of justice. In 1988, Shirley was convicted for murder and sentenced to life imprisonment. One of the matters that the Jury considered, before voting 11 to 1 towards his guilt, was that semen found on the victim was the same blood type as his.

The victim was a young woman. She got raped and then the killer stamped her head and neck. Her body was discovered the next day naked at Merrow Row in Portsmouth. The appellant, was a sailor and the ship he was on had embarked in Portsmouth where the killing took place. Before the killing, Shirley has been at nightclub called “Joanna’s” where usually sailors pick up girls. He picked up a girl who introduced herself as Deena Fogg. However, when they arrived at her house she refused to have sexual intercourse with him, and she left. The Crown’s case was that after getting rejected, Shirley got in a frustrated and angry state and so he raped and then murdered the victim.

Since his conviction, Shirley has been protesting in jail against the decision of the court. However, in 2003, Shirley on a reference by the criminal Cases Review Commission, appealed against his conviction for murder. In order to prove his innocence, he relied on fresh DNA evidence that showed that the semen found on the victim could not possibly come from him. The Court allowed the appeal, ruling that fresh DNA evidence showed that Shirley was not the murderer.

The above cases demonstrate how DNA profiling may prove helpful as an identification tool. As science continues to develop, and passage of time will not contaminate the samples in the DNA profiling process, the law will be comforted by this development and in the future more verdicts where miscarriages of justice has been alleged, may be blamed or justified. Yet even with such a method at hand, the possibility of error -either through human mistake, or through human interference- may not be excluded. That means, that the Courts still will have to value the DNA evidence accordingly to the other facts of a case, and not rely only at the results of the DNA examination.

Analysis of Samples in the Forensic Laboratory

Following the collection of the DNA sample from the crime scene, the DNA sample must go through the profiling process in the forensic lab. Suspects DNA samples will be collected and after the end of the profiling technique the profiles from the suspects and from the crime scene will be compared. If there is no match between these profiles then the profile from the crime stain will be compared with other DNA profiles existing in the National DNA database. In England the first DNA profiling process, known as RFLP20, had been heavily scrutinised. The technical analysis itself was not always accurate and experience has shown that great dangers lie in ambush resulting from its long and complicated nature, as always with new scientific methods;

“The process of DNA profiling starts with DNA being extracted from the crime stain and also from a sample taken from the suspect. In each case the DNA is cut into smaller lengths by specific enzymes. The fragments produced are sorted according to size by a process of electrophoresis. This involves placing the fragments in a gel and drawing them electromagnetically along a track through the gel.

The fragments with smaller molecular weight travel further than the heavier ones. The pattern thus created is transferred from the gel onto a membrane. Radioactive DNA probes, taken from elsewhere, which bind with the sequences of most interest in the sample DNA are then applied. After the excess of the DNA probe is washed off, an X-ray film is placed over the membrane to record the band pattern. This produces an auto-radiograph which can be photographed. When the crime stain DNA and sample DNA from the suspect have been run in separate tracks through the gel, the resultant auto- radiographs can be compared.”21

Firstly, there is a possibility that discrepancies will occur in the number and place of the bands on the comparable auto-radiographies22 of the two DNA profiles. This has been a ground for challenging the reliability of DNA evidence in several cases. Where discrepancies are found in a match, the expert must give a satisfactory explanation with respect to their seriousness. If he fails so, the court may lead to the conclusion DNA evidence is unreliable.

In R v Deen23 the above scenario was demonstrated. Deen was convicted for rape. One of the reasons that made the Court of appeal to order a retrial was that DNA evidence which linked Deen with the rape was inaccurate. In the instant case, a DNA sample was taken from the vaginal of the victim and one from the appellant’s blood. After the two profiles had been compared a match was declared.

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