Witholding evidence from the defence that could help their case or impair the prosecution's by the forensic expert has been known to occur on more than one occasion. Therefore, all forensic evidence must be disclosed to both defence and prosecution, so that they can both question it in court if needed. Sally Clark was a woman convicted of killing her two sons within 2 years in 1999. The pathologist who conducted the autopsies on the boys, concluded during trial that the children had been shaken and smothered.
However, he had failed to mention the fact that microbiology test results on the second baby, Harry, showed the presence of staphylococcus aureus bacterium in his blood, a possible cause for his death, as he had already dimissed them to be irrelevant. However, if he had produced the test reults for the defence, then Sally Clark would have likely been aquitted. Furthermore, it was revealed that the pathologist did not perform all the tests at the autopsy correctly. Accurate results from these properly conducted test may have been vital to proving Sally Clark's innocence.
Due to this evidence coming to attention, Sally Clark was freed in 2003. There are two types of burden of proof in English law; the legal burden, and the evidential burden. The legal burden is the burden of pursuasion, the obligation on the party to prove what it has alleged in court, to the degree of beyond reasonable doubt. For example in criminal cases, the defendant is innocent until proven guilty, and therefore, the prosecution has the burden of proving the defendant has committed the crime, and to disprove any claims made by the defence.
The burden is discharged when the burden has met the standard of proof, which is beyond reasonable doubt, decided by the jury. In discharging the burden, the case is won. The evidential burden is the burden on a party to provide substantial evidence of what has been alleged by the prosecution, before the judge will allow the issue to be heard and examined in court by a jury. There has to be enough evidence to provide a possible conviction – it is up to the jury to decide whether the allegation is true or not. The burden is then passed to the defence, so that they have the opportunity to counteract the allegations and evidence.
There is also the evidential burden to discharge. As the prosecution holds the legal burden, they also must hold the evidential burden. However it is only ever the holder of the legal burden that automatically receives the evidential burden, not vice-versa. The trial judge has to declare the evidence as sufficient for the evidential burden to be discharged. The evidential burden may also be placed on the defendant if they bring the defense new evidence. Any new evidence must be shown to be sufficient to be accepted by the court. This must then be disproved by the prosecution.
In a criminal trial the legal burden usually falls on the Crown Prosecution Service, and therefore the prosecution should hold the legal burden. This strengthens the presumption of innocence until proven guilty, as is stated in Article 6(2) of the European Convention of Human Rights. In the case of Woolmington v DPP , this view was put across by Lord Sankey, when he said; "Throughout the web of the English Criminal Law, one golden thread is always to be seen, that it is the duty of the prosecution to prove the prisoner's guilt subject to…. the defence of insanity and subject also to any statutory exception. "
However, in certain exceptions, legal burden may be placed on the defendant rather than the prosecution, such as in defence of insanity cases, as followed by the legal rules set out by the House of Lords in the M'Naghten's case . Statutory exceptions also affect when the legal burden may be placed on the defendant. However, there are both express and implied statutory exceptions. The Homicide Act (1957) covers an express statutory exception, and imposes a reverse burden upon the defendant, on the grounds of diminished responsibility, where the defendant must prove the crime was committed due to a disturbance of mind.
Furthermore, several provisions under the Terrorism Act (2000), also impose a reverse burden. As stated in s. 101 Magistrates Court Act (1980), implied statutory provisions can impose reverse burdens. Where the definition of a criminal offence includes an “exception, exemption, proviso, qualification or excuse''; the burden lies with the defendant to prove that his behaviour falls within one of the categories of excuse. For example, in the case of R v Edwards , the defendant was accused of riding a motorcycle without an appropriate licence.
The burden of proof lay on the defendant to prove that he held an appropriate licence at the time in question. However, where these exceptions occur, the Woolmington principle of presumption of innocence is contradicted, the defendant appears to be guilty until they prove their innocence.
Jackson, A. R. W. , Jackson, J. M. (2004) Forensic Science, Prentice Hall Keane, A. (2006) Modern Law of Evidence Sixth Edition, Oxford University Press Slapper, G. , Kelly, D. (2004) The English Legal System, Seventh Edition, Cavendish Publishing White, P. (2002) Crime Scene to Court, The Essentials of Forensic Science, RSC