according to Walter, who was Anne Catherick's father? how did he come to that conclusion? give examples from the story

Walter works out from a letter he received from Mrs. Catherick's former employer that Anne was the illegitimate child of Laura's father.

He learns that Fosco has betrayed an Italian nationalist society, of which Pesca is a high-ranking member. When Fosco prepares to flee the country, Walter forces a written confession from him in exchange for safe-passage from England. Laura's identity is legally restored, and the inscription on her gravestone replaced by that of Anne Catherick.