"When it hit me that my correspondent was the same Ted Kaczynski who’d killed three people he’d never met, I felt a shiver of recollection of the fear that prevailed in the Bay Area in the 1970s, during the heyday of serial killers such as the Zodiac, Zebra, Santa Rosa Hitchhiker and Golden State. I was also, to be honest, thankful I hadn’t been rude to him."