Investigators pursuing what they believe to be the largest case of mishandling classified documents in United States history have found that the huge trove of stolen documents in the possession of a National Security Agency contractor included top-secret N.S.A. hacking tools that two months ago were offered for sale on the internet. They have been hunting for electronic clues that could link those cybertools - computer code posted online for auction by an anonymous group calling itself the Shadow Brokers - to the home computers of the contractor, Harold T. Martin III, who was arrested in late August. But so far, the investigators have been frustrated in their attempt to prove that Mr. Martin deliberately leaked or sold the hacking tools. Mr. Martin ... has insisted that he got in the habit of taking material home so he could improve his skills and be better at his job. The material the F.B.I. found in his possession added up to many terabytes" of information ... which would make it by far the largest unauthorized leak of classified material from the classified sector. That volume dwarfs the hundreds of thousands of N.S.A. documents taken by Edward J. Snowden. [Mr. Martin] long held a high-level clearance and for a time worked with the N.S.A.'s premier hacking unit, called Tailored Access Operations, which breaks into the computer networks of foreign countries and which developed the hacking tools.