What type of evidence is provided by a competent live witness speaking under oath?

Testimonial evidence is the type of evidence provided by a competent live witness speaking under oath. This form of evidence comes directly from individuals who recount their observations, experiences, or knowledge related to a case. It is crucial in legal proceedings as it relies on the credibility of the witness, who is legally bound to tell the truth when under oath.

In cases such as fire investigations, a witness might describe what they saw during an incident, provide details about the environment, or explain their interactions with the parties involved. The weight of this evidence can have a significant impact on the outcome of the case, as it can help corroborate or refute other evidence presented.

Demonstrative, documentary, and illustrative evidence serve different roles. Demonstrative evidence typically includes physical objects or visual aids used to help explain aspects of the evidence to a judge or jury. Documentary evidence consists of written materials or recorded information that can be presented as evidence in a case. Illustrative evidence usually involves drawings, diagrams, or photos that provide further clarification of various elements of a case. Each of these has its unique purpose, but they do not carry the same direct personal account that testimonial evidence does, which is why the latter is the correct answer in this context.