Witness for the Prosecution

Christine takes the stand for the prosecution despite being Leonard's wife. She provides circumstantial evidence that reinforces his guilt and fails to offer him an alibi. However, it's later revealed she was deliberately undermining her own credibility to help Leonard get acquitted so she could be free from their marriage.

Earlier, Sir Wilfred notices something suspicious about Christine's demeanor and decides not to call her as a witness, fearing she would harm the defense.

The letters were discovered during a late-night phone call. Christine had written them to a secret lover named Max, expressing her intention to deny Leonard an alibi. The prosecution used these letters to suggest Christine had a motive to frame her husband. However, this actually helped Leonard because the jury believed Christine was framing him out of revenge, leading to his acquittal.

Leonard was acquitted because the jury believed Christine was framing him. The revelation of her letters to Max suggested she wanted to deny him an alibi out of personal revenge. This made the jury doubt the prosecution's case and view Leonard as a victim of his wife's deception rather than a guilty murderer.

Sir Wilfred expresses suspicion about the timing and nature of this evidence, suggesting something is not quite right.

Christine confesses during the final courtroom scene that she deliberately undermined her own credibility to exonerate her guilty husband. Her plan was to appear as if she was framing him out of revenge, which would cause the jury to sympathize with Leonard and acquit him. She did this because she wanted to be free from their marriage.

Sir Wilfred noticed something suspicious about Christine's demeanor when they first met and chose not to call her as a witness.

After being acquitted, Leonard reveals to Christine that he plans to leave her for a younger woman. This betrayal pushes Christine over the edge. In a desperate act, she grabs the knife that was submitted as evidence of Leonard's supposed accidental injury and stabs him to death in front of the shocked courtroom.

Sir Wilfred is a distinguished lawyer fresh from hospital recovery. His doctor has ordered him to avoid excitement. However, when the replacement barrister expresses doubt about Leonard's innocence, Sir Wilfred decides to personally represent the accused himself, driven by his professional instincts and skepticism about the case.

Emily French, a wealthy widow, recently altered her will to leave Leonard a significant inheritance. This is what initially raises suspicions about Leonard's motives, as he stands to benefit financially from her death. The inheritance becomes a key piece of evidence suggesting he had a motive to murder her.

After the jury acquits Leonard based on Christine's letters to Max, Sir Wilfred harbors lingering suspicions about the timing and nature of this evidence. He finds it convenient that such damaging evidence against Christine would emerge at exactly the right moment to save Leonard, suggesting something may be contrived.

After Christine stabs Leonard in the courtroom, killing him, Miss Plimsoll immediately cancels Sir Wilfred's planned trip to Bermuda. She then pledges to assist in defending Christine Vole against the new murder charge, showing her commitment to the legal profession and willingness to help even someone who just committed a crime in open court.

Christine grabs the knife submitted as evidence during the trial. It was originally presented as proof of Leonard's supposed accidental injury from the night of Emily's murder. When Leonard reveals his intention to leave her for a younger woman, Christine uses this weapon to kill him in a desperate act of vengeance in front of the entire courtroom.

The knife was introduced earlier as evidence of Leonard's injury, making it a loaded symbol in the courtroom.