Computer Generated Evidence in Court

Computer Generated Evidence in Court :


We are living in what is usually described as an information society and as the business community makes ever greater use of computers the courts are going to find that increasingly the disputes before them turn on evidence which has at some stage passed through or been processed by a computer. In order to keep in step with this practice it is vital that the courts are able to take account of such evidence. As the Criminal Law Revision Committee recognized the increasing use of computers by the Post Office, local authorities, banks and business firms to store information will make it more difficult to prove certain matters such as cheque card frauds, unless it is possible for this to be done from computers.


The law of evidence is concerned with the means of proving the facts which are in issue and this necessarily involves the adduction of evidence which is then presented to the court. The law admits evidence only if it complies with the rules governing admissibility. Computer output is only admissible in evidence where special conditions are satisfied. These conditions are set out in detail in section 69 of the Police and Criminal Evidence Act (PACE) 1984. In general the principles of admissibility are that the evidence must be relevant to the proof of a fact in issue, to the credibility of a witness or to the reliability of other evidence and the evidence must not be inadmissible by virtue of some particular rule of law.

Real evidence usually takes the form of some material object (including computer output) produced for inspection in order that the court may draw an inference from its own observation as to the existence, condition or value of the object in question. Although real evidence may be extremely valuable as a means of proof, little if any weight attaches to it unless accompanied by testimony which identifies the object in question and explains its connection with, or significance in relation to, the facts in issue or relevant to the issue. This is illustrated in the case of R v Wood (1982) 76 Cr App R 23 where the appellant was convicted of handling stolen metals. In order to prove that metal found in his possession and metal retained from the stolen consignment had the same chemical composition cross-checking was undertaken and the figures produced were subjected to a laborious mathematical process in order that the percentage of the various metals in the samples could be stated as figures. This was done by a computer operated by chemists. At the trial, detailed evidence was given as to how the computer had been programmed and used. The computer printout was not treated as hearsay but rather as real evidence, the actual proof and relevance of which depended upon the evidence of the chemists, computer programmer and other experts involved.

The difficulty in the application of this rule lies in its interaction with the hearsay rule. Evidence is hearsay where a statement in court repeats a statement made out of court in order to prove the truth of the content of the out of court statement. Similarly evidence contained in a document is hearsay if the document is produced to prove that statements made in court are true. The evidence is excluded because the crucial aspect of the evidence, the truth of the out of court statement (oral or documentary) cannot be tested by cross-examination.

The problem, however, occurs because some statements, although in form assertive and inadmissible if they were to originate in the minds of human beings, in fact originate in some purely mechanical function of a machine and can be used circumstantially to prove what they appear to assert. The basis for this view was laid down in a case having little to do with computers. In the Statute of Liberty [1968] 2 All ER 195 a collision occurred between two vessels on the Thames estuary. The estuary was monitored by radar and a film of the radar traces was admitted into evidence. Simon P rejected the argument that the film was hearsay – he held that it constituted real evidence and not hearsay and he placed it on a par with direct oral testimony. Where machines have replaced human beings, it makes no sense to insist upon rules devised to cater for human beings but rather, as Simon P said that the law is bound these days to take cognizance of the fact that mechanical means replace human effort.

This useful distinction was apparently overlooked in R v Pettigrew (1980) 71 Cr App R 39 where the prosecution wished to prove that some bank notes found in the possession of the accused were part of a particular consignment dispatched by the Bank of England. A computer printout was used to prove this but the Court of Appeal held that such evidence was inadmissible under the statutory provision concerned. The Court took the view that the operator did not have the requisite personal knowledge of the numbers of the bank notes rejected from the machine since they were compiled completely automatically by the computer. This conclusion is quite accurate and a perfect application of the hearsay rule but it failed to consider the use of the print-out as real evidence. This confusion between hearsay and real evidence is unfortunate and it may explain why it was necessary to create special rules for computer evidence.

Criminal Proceedings

It is imperative that computer output should be readily used as evidence in criminal cases since otherwise many cases, particularly those involving dishonesty, would be immune from prosecution. At the same time one cannot be too complacent about the technology since computers are not infallible. It is widely acknowledged that hacking and viruses may affect information stored on a computer. These factors were obviously taken into consideration when enacting the provisions governing computer generated evidence in criminal proceedings.

Section 69 of the Police and Criminal Evidence Act 1984 provides that in any proceedings, a statement in a document produced by a computer shall not be admissible as evidence of any fact therein unless it is shown…

(a) That there are no reasonable grounds for believing that the statement is inaccurate because of improper use of the computer

(b) That at all materials times the computer was operating properly or if not, that any respect in which it was not operating properly or was out of operation was not such as to affect the production of the document or the accuracy of its contents.

In addition any rules of court made under section 69(2) must also be satisfied (at the time of writing no such rules have been made). Real evidence and hearsay So far the discussion has focused on exceptions to the hearsay rule. However evidence derived from a computer constitutes real or direct evidence when it is used circumstantially rather than testimonials that is to say when the fact that it takes one form rather than another makes it relevant, rather than the truth of some assertion which it contains.

Direct evidence produced by a computer is not subject to the hearsay rule. As we have already noted, in R v Wood calculations were carried out by a computer specifically for the purpose of the trial to verify whether the composition of stolen metals matched original metals. Computer output was admissible as real evidence since it did not purport to reproduce any human assertion which had been entered into it. It was held that the machine was a tool and that in the absence of any evidence that it was defective, the printout, the product of a mechanical device, fell into the category of real evidence. The court did recognize, however, that the dividing line between admissibility of computer generated evidence as real evidence or hearsay would not always be easy to draw.

The same distinction and result were reached in Castle v Cross [1985] 1 All ER 87 and in R v Spiby (1990) 91 Cr App R 186, CA an automatic telephone logging computer which logged the call details without human intervention was admitted as real evidence. The Court also held that, in the absence of evidence to the contrary, courts would presume that such a computer was in working order at the material time.

Thus as far as the common law is concerned the status of computer evidence as real or hearsay will depend, in each case on the content of the computer record, the reason for using it in evidence and the way in which it was compiled. Cases like R v Wood and R v Spiby, however, must now be read in light of the decisions in R v Shepherd [1993] 1 All ER 225, HL and R v Cochrane [1993] Crime LR 48, CA. In R v Shepherd the House of Lords held that section 69 PACE 1984 imposes a duty on anyone who wishes to admit a statement in a document produced by a computer to produce evidence that will establish that it is safe to rely on the document such a duty cannot be discharged without evidence by the application of the presumption that the computer is working correctly expressed in the maxim omniapraesumuntur rite esse acta and it makes no difference whether the statement is or is not hearsay. In R v Cochrane it was held that before the judge can decide whether computer printouts are admissible, whether as real evidence or as hearsay, it is necessary to call appropriate authoritative evidence to describe the function and operation of the computer. In that case the prosecution wanted to prove that certain cash withdrawals were made from a particular cash point. The machine would only dispense money if the correct Personal Identity Number was entered. The matching was carried out by a mainframe computer and evidence of its proper functioning was thus required by the court. The prosecution did not adduce this evidence and the conviction was set aside on appeal.

As we have seen, a printout from a computer which has been used as a calculating device or which records information automatically without human intervention, is admissible as real evidence and involves no question of hearsay.

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