NEW YORK, N.Y. — Six letters by "To Kill a Mockingbird" author Harper Lee to one of her close friends failed to sell at auction Friday. The archive had been expected to bring as much as $250,000 at Christie's, which said the bidding did not reach the reserve price. Four of the letters date from before "Mockingbird" while Lee was caring for her ailing father, Amasa Coleman Lee, the model for her protagonist Atticus Finch. The signed and typed letters were written to Lee's friend, New York architect Harold Caufield, between 1956 and 1961, according to Christie's, which is selling them on Friday. In one, she writes about her "stunned" reaction to the huge success of the book, published in 1960 and made into a movie starring Gregory Peck two years later. "We were surprised, stunned & dazed by the Princeton review," she wrote.