Why did Mr Lorry, Mr Manette and Lucy are witnesses of Darnay's trial?

Mr. Lorry is called to give evidence against Charles Darnay, and he identifies Darnay as the man who came on board in the middle of the night at Calais on the way from France to England. Miss Manette is called and, though she identifies him, she strongly regrets that her evidence could bring him any harm. Lucie testifies that the prisoner confided in her that he was traveling under an assumed name on a delicate business. Dr. Manette testifies that he also recognizes the man.