His first inkling that something was amiss came in summer 2002 when he opened the door to admit a visitor from the National Security Agency to an office of AT&T in San Francisco.
"What the heck is the NSA doing here?" Mark Klein, a former AT&T technician, said he asked himself.
A year or so later, he stumbled upon documents that, he said, nearly caused him to fall out of his chair. The documents, he said, show that the NSA gained access to massive amounts of e-mail and search and other Internet records of more than a dozen global and regional telecommunications providers. AT&T allowed the agency to hook into its network at a facility in San Francisco and, according to Klein, many of the other telecom companies probably knew nothing about it.
Klein is in Washington this week to share his story in the hope that it will persuade lawmakers not to grant legal immunity to telecommunications firms that helped the government in its anti-terrorism efforts.
The plain-spoken, bespectacled Klein, 62, said he may be the only person in the country in a position to discuss firsthand knowledge of an important aspect of the Bush administration's domestic surveillance program.