What is Giles Corey's proof that Thomas Putnam is reaching out for land and why doesn't he reveal his source?
In Act Three of The Crucible, Gile Corey interrupts the court proceedings to assert that the court has been "hearing lies" and that Thomas Putnam has been "reaching out for land." Corey's wife has been accused of witchcraft and to save her, he puts forth evidence that the girls "afflicted" by witchcraft have been deceiving everyone: a document with an anonymous statement that accuses Mr. Putnam of prompting his daughter to pretend to be affected by witchcraft. Putnam knew that if those accused of witchcraft were found guilty and executed by hanging, they would be forced to forfeit their property; only Putnam had enough capital to make large land purchases in Salem.
Thus, Corey claims to have the statement of an "honest man" who heard Putnam admit this himself. Corey cannot reveal his source because he knows that this "honest man" would be thrown in jail and accused himself if his name were revealed to the public. Unfortunately, without the verification of this person's identity, the courts refuse to accept his testimony.
He says he was told by an honest man about an overheard conversation wherein Thomas Putnam was heard to say that he told his daughter Ruth to cry witch against Mr. Jacobs, his neighbor in order to obtain his land.
Giles refuses to reveal is source because he knows that to do this will probably end up with that honest person being brought to the court and possibly accused of witchcraft as well. By now, Giles and the others who are trying to stop the court from proceeding have seen enough to know that no one is safe from an accusation of witchcraft, and he is not willing to endanger his source in this way.