The third alternative is correct.
The judgement is composed of several stages, ranging from the opening of the process to the final verdict of the judge. In a judgement, both parties have the constitutional right to full defense and a fair trial. Each party makes its considerations about the facts in judgment. Moreover, witnesses are summoned who can tell everything they know before judgment. After the witness's speech, a period of interrogation is opened, where the lawyer can question the witness's allegations when he or she considers that there is some kind of contradiction. Therefore, it is at the cross-examination stage that the credibility of the witness can be undermined.