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.