Impeachment of witnesses is the action of calling into question the integrity or validity of an individual testifying before a court during a trial. Under the common law, this process would involve introducing circumstantial evidence to suggest likelihood that the witness may give false or an incomplete testimony.
The process of witness impeachment is supported by various laws in Kenya. As for example, the Evidence Act explains who can impeach a witness, and how the process for achieving an effective witness impeachment exercise can be done.
The purpose of impeaching a witness is to show that the witness is lying about a material fact that is aimed at hurting an accused or a plaintiff’s case. Impeachment serves to discredit a witness’s testimony to the effect that the court has to disregard it or give it less probative weight.
During the cross-examination of witnesses they may [in addition to the questions asked during cross- examination] be asked any other questions which tend to test the accuracy, veracity or credibility of testimony given to court. They may further be questioned as to their identity all in furtherance of shaking their credibility and injuring their character.
Hon Justice Sergon noted in Law Society of Kenya v Faith Waigwa& 8 others (2015) EKLR that cross- examination of witnesses is intended to impeach their credit worthiness. During this cross-examinations, a witness may be asked questions tending as for example to expose errors, contradictions, omissions and improbabilities in their given testimony. In the process, the veracity of a witness’s averments is tested.
If a witness testimony is then harmful to the case, one will then seek to challenge their evidence as inconsistent, improbable or unrealistic. However, to note is that witness impeachment can only be done during cross-examination.
However, pursuant to the Browne v Dunn Rule, before one attempts to impeach a witness, they or their trial advocate must be in such a position to prove what they allege just in case the judge will require verification of those facts. This rule is aimed at protecting the witness from attacks predicated on unverifiable facts.
Grounds of impeaching a witness
A witness may be impeached on the following five grounds:-
1. Impeachment based on prior inconsistent statements.
Section 155 of the Evidence Act states that witnesses may also be cross examined on a document they produced as evidence or on a previous written statement. However, if the intention is to bring out a contradiction between what they said under oath and what is contained in the written statement, the same must be shown to the witness such that they confirm the contradiction observed.
2. Impeachment on grounds of inducement
Here the examiner be it a lawyer, the plaintiff or accused has to prove that the witness has bias against a party, motive and interest in the outcome of the case.
Under this approach, evidence is brought to show that a witness has bias for or against a party, financial gains, motive and interest in the outcome of the case. Credibility of key witnesses is important and evidence showing that they are biased will form a basis of such prejudice.
3. Impeaching by calling another witness
Though rarely used in courts, Section 163 provides that the credit of a witness may be impeached by the adverse party during the cross examination stage.
4. Impeachment as to credibility
A witness is impeached by asking questions that seek to attack their credibility. Section 158 of the Evidence Act provides that questions attacking the credibility of a witness shall only be permitted if the person asking the questions has reasonable grounds for thinking that the imputation is well founded albeit court has the discretion of forbidding questions which it considers scandalous, indecent, insulting or annoying.
5. Impeachment based on the character of the witness
As defined by the Evidence Act Character includes both reputation and disposition. Section 56 of the Evidence Act provides for bad character in criminal cases. It states that ‘ In criminal proceedings, the fact that the accused person has committed or been convicted of or charged with any offence other than that which he is then charged, or is of bad character, is inadmissible unless the set out exceptions are satisfied.
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