how does Giles not help his case? copy his quote

Giles is a fiery old man by nature. In act 3 he bursts into the courtroom and angrily says to Judge Hawthorne, "You’re not a Boston judge yet, Hathorne. You’ll not call me daft!" As well Giles accuses Putnam of killing neighbours for their land. He claims he heard proof but will not name his source,

The proof is there! I have it from an honest man who heard Putnam say it! The day his daughter cried out on Jacobs, he said she’d given him a fair gift of land.

Hathorne: And the name of this man?

Giles, taken aback: What name?

Hathorne: The man that give you this information.

Giles, hesitates, then: Why, I - I cannot give you his name.