How is Giles’ deposition turned against him in The Crucible?

Giles Corey's deposition states that Mr. Putnam told his daughter, Ruth, to accuse George Jacobs of witchcraft so that Putnam could buy his land (which would go up for auction upon Jacobs's conviction).  Corey says that "none but Putnam [has] the coin to buy so great a piece."  When Danforth asks for proof, Corey points to his deposition and says, "The proof is there!  I have it from an honest man who heard Putnam say it!"...

Giles Corey's deposition states that Mr. Putnam told his daughter, Ruth, to accuse George Jacobs of witchcraft so that Putnam could buy his land (which would go up for auction upon Jacobs's conviction).  Corey says that "none but Putnam [has] the coin to buy so great a piece."  When Danforth asks for proof, Corey points to his deposition and says, "The proof is there!  I have it from an honest man who heard Putnam say it!"  However, Corey will not tell Danforth the name of this "honest man" because he knows the man will end up in jail if he reveals his identity in front of Putnam.  Danforth believes, though, that if he were a "decent man," he would come openly to the court with his evidence; if he would "hide in anonymity," then Danforth believes that he has other motives in accusing Putnam of being "a common murderer."  When Corey continues to refuse to give the name, Danforth arrests him "in contempt of court" and threatens him with jail.