that before in my career except something similar on tv. >> reporter: one thing about that strange letter was all too obvious. whoever wrote it had inside knowledge because nobody besides the cops knew what the atf had discovered. >> we hadn't told anybody it was a bomb so for somebody to just write a letter claiming responsibility for a bombing, that lended credence to the fact that the author of that letter was the real thing. >> weird. all too weird. detective salm and the others went home for the weekend to digest what they had read and seen. then, monday morning his phone rang, 7:00 a.m. >> hey, we got another one of those letters. i came to work. there was a second letter sitting on my desk. this one was slightly smaller manila envelope or half size. but configured the same way.