The law which governs the rules of evidence is very complex, and its importance in considering the best strategy to adopt in every case cannot be over emphasised. Many cases are won in court because of a superior knowledge of its applicability. Generally in Scotland, evidence has to be relevant and competent before it can be admissible. A solicitor has to know when to raise an objection to inadmissible evidence otherwise it could be allowed in by the court.
There must also be a legal sufficiency of evidence before an offence can be proved. Every offence other than certain minor road traffic offences has to be proved by way of corroborated evidence: that is by two sources of evidence. This means that a conviction cannot be secured by way of evidence from one source alone. Two sources of evidence are required to prove that a crime has been committed, and also the identity of the perpetrator. Such evidence can come from a variety of different sources such as eye witness evidence, CCTV footage, DNA , admissions by the accused, documentary evidence, and voice recognition. Before any of this evidence can be admissible it has to conform to complex evidential rules.
A crime can be proved by circumstantial evidence which mounts to various strands of indirect evidence which individually do not amount to much but when taken together provide a strong body of evidence. It is important to ensure that this evidence is scrutinised with care and tested properly in court to expose important failings in the Crown case.
Although it is for the Crown to prove guilt against an accused, very often an accused is able to produce exculpatory evidence which can support their defence. It is important that this evidence is identified and secured at the earliest opportunity so that it can be used in evidence in court. Often this evidence can be presented to the Crown before a trial to persuade them to discontinue the prosecution.