Witness

witness is someone who has, who claims to have, or is thought, by someone with authority to compel testimony, to have knowledge relevant to an event or other matter of interest. In law a witness is someone who, either voluntarily or under compulsion, provides testimonial evidence, either oral or written, of what he or she knows or claims to know about the matter before some official authorized to take such testimony.

A percipient witness or eyewitness is one who testifies what they perceived through his or her senses (e.g. seeing, hearing, smelling, touching). That perception might be either with the unaided human sense or with the aid of an instrument, e.g., microscope or stethoscope, or by other scientific means, e.g.,a chemical reagent which changes color in the presence of a particular substance.

A hearsay witness is one who testifies what someone else said or wrote. In most court proceedings there are many limitations on when hearsay evidence is admissible. Such limitations do not apply to grand jury investigations, many administrative proceedings, and may not apply to declarations used in support of an arrest or search warrant. Also some types of statements are not deemed to be hearsay and are not subject to such limitations.

An expert witness is one who allegedly has specialized knowledge relevant to the matter of inter