What does Ellen reveal at Philip's trial when Waleran accuses her of perjury?

Ellen tells the court that Waleran is the perjurer. She relates the sad tale of Jack Shareburg, imprisoned unfairly and ultimately given a jeweled cup and set free. Jack had left the cup behind at Kingsbridge, but when Waleran arrested Jack, the cup had mysteriously appeared again in Jack's possession. She accuses Waleran Bigod, Percy Hamleigh, and Prior James of Kingsbridge of giving false testimony that resulted in the hanging death of Jack Shareburg.