In Act Three, Giles Corey presents his deposition to Deputy Governor Danforth which states that Thomas Putnam prompted his daughter to accuse George Jacobs of witchcraft in order to take his land. Putnam denies the accusation, and Danforth asks Giles Corey for proof. Giles Corey maintains that he has an honest man's testimony, saying that he overheard Thomas Putnam tell his daughter to accuse Jacobs of witchcraft in an effort to buy the forfeited land. When Hathorne asks Giles to give him the name of the man who overheard Thomas Putnam's conversation, Giles refuses to state his name. Giles Corey does not give the man's name because he knows the Court will have the man thrown in jail. Giles is not naive and does not want to implicate another person in the witch trials. He already mistakenly mentioned his wife and feels extremely guilty about it. The citizens of Salem also fear the court and do not want to openly speak out against it.
The deposition that Giles Corey presents to Danforth includes the account of a man who heard Putnam say that by getting his neighbour killed for a witch he would be able to buy the land at a cheaper price. However, when pressurised by Danforth to give the name of his witness, Giles Corey refuses. It is easy to understand why he is so unwilling to give the name, as he has already mentioned the name of his wife before and she has been jailed as a result. Note how he explains his refusal to give the name of his witness to Danforth:
I will not give you no name. I mentioend my wife's name once and I'll burn in hell long enough for that. I stand mute.
The witch trials have advanced so far by this stage of the play that to even have your name mentioned as questioning them is enough to send you to jail directly for questioning. This is of course something that makes it very difficult for John Proctor, Giles Corey and Francis Nurse to oppose what is happening.
Because they fear that in the Witch hysteria that if they do they will be accused of witchcraft.