What is the purpose of cross-examination?

Answer 1

In our legal system, cross-examination of witness testimony is designed to contradict the viewpoint of the opposing counsel. For example, if direct examination of a witness in a murder trial had a question that asked "Did you see the defendant at the crime scene?", defense counsel on cross-examination might ask questions about the witness' eyesight if he/she wears thick glasses or has other vision problems to cast doubt in the jury/judge's mind whether or not the witness did in fact see the defendant.

In criminal cases in a jury trial, or even a trial in front of a judge only, all questions on cross are designed specifically to cast "reasonable doubt" on the prosecution's case. Civil cases are different in that all that is needed is a preponderance of evidence to show guilt.

Answer 2

To ask for clarification, to expose weaknesses in the argument or evidence, to discredit the witness, or to elicit facts favorable to the party the cross-examiner is representing.

"Indeed, cross-examination is arguably the essential, if not sole, purpose of a criminal trial. Opening statements, the importance of which so many lawyers underestimate, is the foundation of effective cross-examination. The opening is where the lawyer not only provides the jury with the defense's version of the facts, but details how he will cross-examine prosecution witnesses. If the lawyer wastes the invaluable opportunity afforded by the opening, leaves critical "facts" unchallenged, neglects to cite examples of the witness's duplicity, and fails to tell the jury how he will cross-examine the witnesses, it's unlikely the jury will grasp the significance of otherwise effective cross-examination."