US prosecutors have withdrawn a subpoena seeking the identities of thousands of people who bought used books through online retailer Amazon.com Inc., newly unsealed court records show. The withdrawal came after a judge ruled the customers have a right to keep their reading habits from the government. "The (subpoena's) chilling effect on expressive e-commerce would frost keyboards across America," US Magistrate Judge Stephen Crocker wrote in a June ruling. Federal prosecutors issued the subpoena last year as part of a grand jury investigation into a former Wisconsin official who was a prolific seller of used books on Amazon.com. They were looking for buyers who could be witnesses in the case.