In 2006, a retired AT&T engineer knocked on the door of the EFF's office in a rundown part of San Francisco's Mission district and asked, "Do you folks care about privacy?" With him he carried schematics exposing the largest US government domestic spying operation since Watergate.That person was Mark Klein, who died on March 8 this year from cancer. He was 79.After a life working in telecoms, Klein realized he had helped the NSA wire up a listening station in AT&T's San Francisco switching facility - the infamous Room 641A - that was being used to illegally spy on Americans.The evidence he gathered and shared led to two lawsuits that exposed the extent to which US citizens were being spied on by their own government in the post-9/11 world. Klein faced legal pressure, death threats, and the constant fear of ruin, to get his story out and tell the public what was going on. But Klein regretted nothing."He was very much aware of this history in our country of the government's secrets and wars," his brother Larry told The Register."The idea of wiretapping our own people really bothered him, and he found himself working for a company that's intercepting emails and conversations. I'm very proud of him, very, very proud of my brother. I always think I want to have the courage to do what he did, to tell the truth."The secret roomIn 2003 NSA operatives came to visit the AT&T offices at 611 Folsom Street. They were assigned Room 641A and started to install their own equipment connected to the telco's network to monitor communications. It relied on fiber optic beam splitters that made a copy, effectively, of internet backbone data flowing through AT&T for the Feds.One unusual aspect of the installation was that the NSA wanted only non-union AT&T staff to work in there for installation. Klein was a solid union man but had skills that were needed - Klein spent over a quarter of a century as a telecoms engineer and was a master of the craft.When the operatives ran into problems installing some equipment they called him in and he helped install the splitters that would direct data into the inspection servers in Room 641A. This wholesale routing of information worried him enough that he kept documents showing how the wiring worked just in case.Then in 2005 the New York Times finally published a story it had been sitting on for years. Shortly after the 9/11 terrorist attack the Bush administration had decided that domestic spying laws were inadequate and had let loose the intelligence hounds.The NSA and other agencies went to telcos and demanded the right to surveil citizens and to store data of phone and internet use. The Times had first learned of this shortly after the decision was made but agreed to keep the news under wraps on national security grounds.When the story was published, Klein realized what he had done - he had helped wire up the surveillance state and he was furious about it. He still had the documents about Room 641A though getting the word out about the system proved frustratingly difficult.He went to one newspaper, which strung him along for months promising a big front-page splash and then spiked the story. Other media outlets refused to touch it, although he did get some TV time (see below). Having heard about the EFF, which also had the bonus of being in San Francisco, he decided to drop in unannounced.Youtube Video"He literally walked up to our front door and rang the bell, and said, 'You folks care about privacy?' and we said 'Yes we do,'" recounted Cindy Cohn, now the executive director of the EFF, to The Register."It took us a little while to really recognize that he was the real deal. But he had all these documents with him, and we pretty quickly sent them off to people we knew who had a much deeper understanding of communications networks than we did. And they said, 'Yeah, these look legit.'"Enforcing the lawArmed with his insider information, the EFF helped file two lawsuits; Hepting v. AT&T, and Jewel v. NSA. The first was a class-action lawsuit on behalf of AT&T's customers who may have been surveilled by the NSA system. The second was a case directly against the NSA for carrying out the then-illegal spying.The Hepting case looked like a slam dunk, and claimed AT&T had clearly broken the law. As a result, Congress changed the law and retroactively granted telcos immunity if they conducted wiretaps in the interest of national security.Jewel v. NSA was also dismissed, on the technicality that the individual complainants couldn't prove that they had personally suffered harm for being surveilled. The NSA wasn't going to tell them the details so the case fell by the wayside."He was really upset about it," Cohn said. "He was a technologist, you know, and he was a creature of that world."We spent a week in Washington DC together lobbying and he was the kind of person who thought if you showed up with all the facts and you laid them out in front of smart people they would do the right thing. I don't think he ever really got over the fact that that wasn't true and that doesn't happen."He wrote a book about his experiences, Wiring Up The Big Brother Machine And Fighting It; it's a cracking read.Klein settled into retirement but was always willing to talk about the NSA's interception. Your humble vulture interviewed him in 2013 after the Snowden disclosures, and he was fascinating to talk to, incredibly knowledgeable and calm, yet forceful."He was determined to follow through with it all," his brother recounts. "We'd grown up with the Vietnam war and he admired Daniel Ellsberg and the leaking of the Pentagon Papers. He really was worried about the power of the President, and other cases around the world, like Assange."On March 8, after a prolonged bout of prostate cancer, Mark Klein passed away at his home in Oakland, California. The example he set was an admirable one, Cohn said."I'm just devastated that we weren't able to get Mark justice during his lifetime. So I feel like the least we can do is honor him," she said.