walls that came crumbling down on brandon mayfield. when did you first have a sense that you and your family might have been subject to direct surveillance by the government? >> a footprint on the floor that were bigger than any shoe size we had, so we could only surmise somebody had been in the house. >> mayfield and his wife, mona were living a quiet life, but in may 2004, after weeks of secret government search and surveillance, federal authorities come knocking on mayfield's door. >> i said if you have any question to ask me, put them to me in writing, and i could tell right away that wasn't going to make them go away. >> in march 2004, a terrorist attack on trains in madrid, spain, have killed 191 people. spanish police found a fingerprint near the scene on a bag of detonators.